While I understand the suggestion to only adjust and fix what is broken, I think that mainly applies to newbies. It's a good stepping stone to learning how to go completely through a game. Which most 40-60 year old games are going to need in my opinion.

Generally if one stepper is gummed up and your initial problem, they all could benefit from a disassembly and cleaning. If one score reel is hanging up, they could probably all use some attention. The few games where I have only fixed what was broken usually resulted in chasing other problems later.

That's a fair analogy. Another consideration is if the game was recently shopped or serviced. If so fixing individual components makes more sense. My typical game comes home with years of neglect so it requires a more thorough approach.