OP

Quoted from jfoust:

Update for everyone - I finally got to spend some time going through the machine a few days ago after studying the manuals, etc. Here's where things went:
1) I dissembled and cleaned all steppers. This did nothing to improve things, but it was probably a good thing to do on a machine of this age, and now I know how they work, and know that they are clean and functioning as they should.
2) rolf_martin_062 was correct - turns out one of the switches on the Game Over relay wasn't making good contact. It was close enough that as I went through the switches the first time, it appeared okay, but on closer inspection, it was not quite closing well enough. Adjusting that switch got most everything going, and got the game to always start up in 'game over' mode instead of starting mid-game, or not starting at all.
3) I also found the wire that goes to the playfield feature lights from the Tilt Relay was loose, and popped off at some point. Clipped, stripped, and re-soldered those wires, and now everything works there.
So we're playing games start to finish just fine now!
My next issue that I've discovered now that I have a working machine, I haven't quite managed to solve yet:
When your bonus is totaled at the end of a ball, it's not adding all the points, but it only has a problem in single bonus mode. Example - if you have 10,000 points, and the 5,000 bonus is lit in single bonus and you drain, you end up with usually 13,000 or 14,000 points. In double bonus, you end up at 20,000 just like you should, and triple bonus works as well.
Also you'll randomly start a ball with double bonus lit, and every now and again triple bonus. This might be happening one out of 12 balls or so, and it's not necessarily happening if you had double bonus on your last ball., so it's not like something gets stuck on.. Any thoughts as to what could cause these two issues?