On the Gottlieb Flipper Mechs they went to on some of the later games (ex: 1977 Big Hit, 1977 Jacks Open, etc.) it's well-known that the set screws that hold the flipper shaft to the mechanism that turns can often be stuck in the hole and brittle.
I have been having problems lately where, although I'm able to get those screws back out, once I put them back together and in the holes, they start to back out a little bit and then the flipper shaft doesn't turn when the mechanism turns.
I am not sure if this is because:
A. I'm not tightening them enough (perhaps because I fear them breaking off, as they're known to do
B. Somehow the holes have just been warbled out slightly larger through the years and they're not in those threaded holes tightly.
I am wondering if the community has had experience with this and found a good solution. I was thinking of taking them out, applying some Lock-Tite or another product to the screws, and then putting them back into the holes tightly.