Fact #1 - anything (and I mean anything) that has any kind of mechanical moving parts is going to at some point in it's life break down.

Fact #2 - pinballs have many mechanical aspects to them.

Fact #3 - there is nothing you can do to change Fact #1.

Also mentioned that "you bought junk" - well if that was the case, it will take a good amount of time to strip down the machine and go through it all and replacing and checking it all out. If you have not done so and are one that just deals with an issue when it becomes unplayable then you are only hurting yourself. Remember, the games you list are around 20 years old already. 20 years is a long time for anything mechanical.

I have seen this many times in the car hobby (my other hobby) - people buy an older car cause it is cool. Car breaks down, which older ones will do, just a matter of when. They 'fix' it with some 'duct tape and bailing wire' to get it going and figure it's good enough (or the problem is ignored as they can "drive" the car). Down the road the problem becomes more serious, so more patch work, again leading to another issue down the road and then all of a sudden the car becomes a POS. I know 1 fellow right now, thinks here can rebuild an engine and has done so, engine does run but he says it shakes severely at idle. But get this, he says it 'feels' just fine while not at idle/driving and is not concerned over that "small issue". I give it a few months before it is dead (once again).

Pinball related - I recently bought a Getaway myself. The PO thought it worked just fine and had "no issues" with it. Let me tell you that IMHO there are a few things wrong with it that I point out - DMD on it's way out, issues with a couple switches not working (game would tell you to do a test report when turned on), ramp in back not working correctly, ball shooter not working correctly, burnt lamps. All of which he didn't notice (or care) as the game still "played". Plus the fact that he only has the games to play and has no interest in repair/maintaining them, which was good for me as I got a deal on it.