Cleaning up the steering wheel turned out to not be such a hard job.
The alloy central boss had been the subject of a terrible paint job at some stage of its life, and the plastic rim was cracked in a number of places, but all in all it was salvageable.
I used a two part epoxy to fill all the cracks in the outer rim, and after about three rounds of filling (it’s amazing how some of the cracks hide themselves) a bit of hand-sanding had it looking nice and smooth.
I used a fine wire brush on the angle grinder to get rid of the crap on the boss, and get it back to bare metal. I followed it up with a very fine wire brush on the Dremel to get into the corners, and to clean up the chrome spokes.
After masking off everything except the boss, I sprayed the alloy with etch primer, and the steel section surrounding the horn slider with plain primer, then gave the whole centre a coat of gloss black enamel.
There’s a bit of advice around the web about how to deal with the rim. Eventually I settled on putting on a coat of Septone Plastic Adhesion Primer, and followed it up with several coats of Septone Vinyl Spray Paint. It looks really good now, but only time will tell if the vinyl paint has any longevity.
This is the wheel with the rim filled, and the centre painted black.

And here’s a couple of pictures of the finished wheel.

