One of the first things I would do, spend an hour or so with a points file or 600-1200 grit wet/dry sandpaper and go through every relay and contact set, cabinet, playfield both sides and backbox.
While doing that check the contacts to make sure the relays move easily, and the contacts travel a tiny bit more than just barely touching.
That will revive most problems.
Second, check the steppers by pressing the relays to ratchet them back and forth. It should be smooth. If they are very sticky, a few drops of oil can help in troubleshooting to loose things up, but they will need to be disassembled and cleaned if they’re gummed up.
While checking the steppers, some contact cleaner on cue tips or pure isopropyl alcohol for electronics on cue tips to white the sliding tracks and sliders will revive those contacts.
Don’t forget the score wheels as well.
It will be a couple we’ll spent hours that will end in a mostly running pin with much less left to debug.