I just restored a 1964 Gottlieb Big Top (and I must get around to doing a restoration thread on it.) The disc on the Balls to Play stepper had about a dozen rivets with deep grooves cut through them and that was causing the Balls to Play display on the backglass to work intermittently.
I thought I'd try the silver solder solution. The project was one that I thought would take a few minutes, as I'd intended to fix a dozen rivets. It ended up taking about three hours, but produced good results.
My disc had 50 rivets and about 12 had deep grooves cut in them.
1. I identified the dozen or so rivets that needed attention. I put a dab of flux on each rivet.
2. I used a soldering iron to put a small drop of solder on each of the rivets. My silver solder was rather thick in diameter, which made it difficult to get a drop of solder that wasn't huge. I ended up using wire cutters to cut small (1/8" long) pieces of solder, which I had on a piece of cardboard. I'd touch a piece with the soldering iron, let it melt, and then I'd transfer it to the rivet.
3. Once done with the dozen rivets, I now had 12 rivets that were taller than the other 38.
4. I decided to add a drop of solder to all 50 rivets.
5. Once done, all of the rivets were too high, and the stepper couldn't move over them. Now I had a stepper that didn't work at all!
6. I got out my Black and Decker Mouse sander with 80 grit sandpaper and sanded all 50 rivets down to a uniform height.
7. I wiped the board down with a cloth and some Novus #2 to get rid of the dust.
8. I applied a light coat of Super Lube to the disc.
9. I reassembled the stepper. All good.
I've now got a stepper where all 50 rivets are uniformly sized and have no wear. The game now works properly.
Silver solder is surprisingly tough stuff, so this looks to be a solid repair. None of the silver solder drops broke loose during the sanding. One thing to watch out for is to make sure that the wires on the back side of the rivets don't come loose when you're applying heat to the worn side.
A good, inexpensive solution to a common problem and as DirtFlipper said above, it's one that will probably last for years.