One of my recent restoration projects was on a Scalextric March Ford, where the rear chrome motor section had several parts broken off. This page shows you step by step how I restored it back to something close to the original shape. Unfortunately, I neglected to take a good photo of the "before" piece, but it was missing the exhaust pipe and bracing arm on the left side and the radiator fin and support and linkage arms on the right. This piece was repaired using some 1/8" plastic tubing and a piece of "H" channel (from which I cut out all the arms and other pieces), for under $7 from a local hobby shop, and glued together with a 2-part epoxy glue called "araldite" here downunder.

Step 1. Rebuild Exhaust This was the simplest repair. I filed the broken end of the exhaust square, then measured and cut a piece of 1/8" tubing to fit. Then measured and cut the plastic support arm from one side of the H channel. To reinforce the joins, I drilled a fine hole 1/8" deep into the broken off exhaust section, and glued a 1/4" bit of brad (very small nail), into the hole I drilled, then glued the piece of tubing over the top. I also cut out a very small piece of the tubing where the support arm meets it, and embedded the arm into it, to strengthen that join too.
Step 2. Supports for Radiator Fin and Linkage Arm It is difficult to see from the pic, but the fin broke off and took with it a triangular section of the part on which it sits. I had to cut and file a piece of thicker (blue) plastic to shape and glue that in place first to give the fin a level resting point and fill in the gap. At the same time, I also cut and shaped a small piece of plastic to replace the broken vertical linkage section. I deliberately made this piece a little thicker than the broken off section, so it had an extra bit of an overlap for reinforcement, otherwise I would have had a very small gluing surface.
Step 3. Attach New Fin The next step was to make up a piece for the fin. I couldn't easily reproduce the textured finish, so didn't even bother trying. I was not trying to make a perfect reproduction, just approximate the original shape. This is where one of those handy little gadgets with the heavy base, easily positioned alligator clips and magnifying glass really pays for itself, holding the fin in position till the glue dries (several hours for this stuff).
Step 4. Attach Support and Linkage Arms The final piece of manufacturing was to make up a couple of strips to replace the 2 support/linkage arms coming from the top left and bottom right of the fin. I cut out little sections in the fin where they joined to strengthen the joins, rather than relying on a flat join.
Step 5. 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.
The finished product - installed!
What it should look like (My only other complete one)