My current restoration project is to restore several Scalextric AC Cobras. One was in good condition almost complete, just missing the exhaust pipes, the second was in reasonable condition, missing windscreen, exhausts, wheels and guide, but the third was just the body which was in a real mess, with all trim but the roll bar missing and the rear arches cut out drastically and roughly.

This page shows you step by step how I am restoring the worst one back to almost original condition. I will make extra parts as I go, to finish off the other two as well (plus some extras for spares in case of future breakages). The missing pieces I made from some 1/8" half round plastic rods, 1/8" tubing left over from previous restores, some 1mm plastic rod and a clear plastic sheet.All these together cost under $20 from a local hobby shop, and I have only used a small fraction of the stock so far, so there is plenty left for future restores.

This shows the three Cobras as at the start, to show what they should end up like. The 2nd Cobra in this photo already has my custom built windscreen installed, and I had started to rebuild one of the wheel arches on the 3rd.
What the worst one looked like. You can see the gauged out rear arches. I stripped off the tonneau cover, and stripped the paint off the driver, in preparation for eventually repainting the whole car, to hide the repairs to the arches. Not sure whether to paint it green and reproduce the Scalex green version, or paint it dark blue to reproduce an actual racing version, with the big white stripes.
Windscreens As I had one good windscreen, I was able to make up my own screens using it as a template. Fortunately, the Cobra windscreens were basically flat, with only one sharp bend required at each end for the wrap around section. The first attempt wasn't much good, but it gave me a template from which I could work with to correct the mistakes. Rather than cutting and joining, I made each windscreen from a single piece of the clear sheet, using boiling hot water to soften the plastic so it would retain its position once bent into the correct shape.
Exhausts These were not too difficult, as again I had one good one to use as a template. They were basically straight sections of half-round plastic, with a right angled pipe section stuck on the end. I made one up to match the good one exactly, but made the rest with an angled pipe, as that more closely resembled the real versions. This is what they should look like.
Step 1. Cut and shape base sections Measure out and cut off a section of the half round stock. One end is rounded off. Mark and drill the first 2 holes on the back flat side for later fitting of the lugs used to position and hold the exhaust in place. The 3rd hole is drilled all the way through, as it is used both as a locating lug, and also to reinforce the join of the pipe section. This can be drilled at 90 degrees to duplicate the original shape, or at an angle to resemble the real thing (the lug can be straightened later on).
Step 2. Shape and cut the end pipe section. To replicate the original shape, you need to file the 1/8th tubing to a slight cone shape. This is best done before cutting it off. Once it is cut off, you need to use a small round file to shape the bottom end of the pipe to fit over the half-round stock. Again, this needs to be done at the correct angle, depending on the look you want to achieve.
Step 3. Glue it all together. As all these parts were manufactured from polystyrene, I could use a normal plastic cement, which is a lot less hassle and sets much faster than epoxy. The lugs are glued in place first. If you can find a drill tube stock such that the hole is a fraction too small, all the better, as the tighter the fit, the better the result. I used a 1mm drill and 1mm stock, as that was all I had available. Using a drill stand will give you a more accurate right-angle and a tighter fit, if you have one (seems an overkill I know, but if the tubs stock fits in tightly enough, you may not even need the glue). The 3rd lug needs to go right through the half-round section, and the little pipe section is glued over the top of it, to provide a stronger reinforced join.
Step 4. Spray with a Chrome finish Paint Unfortunately, unless you have access to chrome plating equipment, the closest you can come to a chrome finish is a good quality spray paint. At least it makes it look like a single piece again.
Finished 2nd Cobra I stripped and repainted the driver, as he was a bit scruffy, detailed the steering wheel, attached the new exhausts and windscreen, added wheels (non-std), bought some repro decals and here's how she looks. Good as new!
Wheel Arches The 3rd Cobra's wheel arches had been cut out quite severely. I used a tamiya 2-part epoxy putty to try to repair these.
Step 1. Attach rough mould Made up a thick snake like section and pressed it into the arch, making sure there was a good solid contact on the inside, and small thin overlap on the outside. Then roughly shaped it to match the flaring of the original guards. Once it sets properly in a few day, i used a sharp stanley-knife to cut the shape of the arch, and to trim the outside and inside walls to the desired thickness.
Step 2. File and sand to shape Using a small half-round file and a fine round file, started filing back the outer part of the mould to required shape. Need to make the top part of the mould flush with the body, but leave the bottom edge flared. Used half-round file first to smooth the mould and get it flush, then used the fine round file to shape the flare. Finally used two very fine grit emery papers to sand the mould to the final rounded shape and smooth it all off.
Step 3. Repeat on Other Side After repeating the repairs on the other side, I also went over the whole body, sanding off old scratches, marks and lines left from the original mould, to ensure a perfectly smooth finish.
Step 4. Repaint to Hide the Repairs I dedided to repaint this in a very dark blue (the pics look lighter than the actual result), to reproduce an actual AC Cobra I've seen pics of. This will show how well you have smoothed off the repairs, as the paint will show up any blemishes. I could only find one small blemish on one guard, so decided it wasn't worth redoing.
Headlights The 3rd Cobra also needs headlights. I am going to try making these out of clear plastic sheeting.
Step 1. Drill and Cut Rough Wheel Trust me, its a lot easier to mark your circle, drill the hole for the rod, and then cut around it later, than to try to hold a tiny piece of plastic in place while you drill it horizontally. Best to use a drill stand if you have one to make sure you get the hole perpendicular. Don't drill all the way through, stop about a mm short of the full depth, so you get a nice clean front surface.
Step 2. Attach Spindle. Because this will need to take a fair amount of force during the filing stage, I found it best to choose a drill size slightly smaller than the rod. You will be limited by the thickness of the clear plastic rods that are available though. I think mine was 3.1 mm rod into a 3mm hole. You then need to taper the end of the rod a little, so you can tap it it into place. I used a plastic cement as well, but I think the tight fit and a good tap with a hammer provides the strength you need. Don't hit it too hard or have too big a difference in the diameters, or you may shatter the plastic.
Step 3. Sand/File to the Required Diameter This is where one of those Dremel like tools are great. Mine was cheap $14 copy from Bunnings, and it works great. Just put the spindle into the tool, turn it on and slowly work it over rough emery paper or similar. Go slowly here, or you can melt the plastic. Just keep working it down slowly until you reach the desired diameter for the headlight. Cutting your blank close to the fiished size will save you time, but does not leave much margin for error.
Step 4. Round Off Headlight & Polish Smooth When you have the desired diameter, start working the edge and top of the headlight to give yourself the desiired roudned shape. When you have the shape you want, start working your way down through 3 or 4 finer levels of emery paper (or wet & dry), until you get to about 1500. It will look a bit fogged, but this can be polished off with a fine car polish (I used Kitten No.1 polish).
Step 5. Finished product Before you cut the spindle down to a length long enough to fit through the hole in the body and be glued or melted into place, you should file down the spindle to its desired thickness. The hole in the body if likely to be narrower than your rod size, unless you can find a perfect match, and its a lot easier to do while its still in the tool. It will look better on the car it you paint the rear of the headlight silver/chrome, and maybe even the outer rim of the headlight.
Finishing Steps   Here is the finished body with the headlights, filler cap, exhausts, roll bar and driver head attached. I have also detailed the body, by painting the steering wheel & spokes, the front indicators, the rear boot catch and the front grill.
The Rear Angle
The Finished Car Here is the finished product. I coated the body with the Aussie equivalent of Future, Pledge One-Go, and then applied my own decals, which I made up using laser labels on a laser printer at work. I know the wheels are not correct for this model, but they were the only ones I had.