So, when I picked up my machine the old owner said it was giving him a "1 ball missing" error when it was turned on. Although clearly there were 6 balls in the game. He told me this up front as it's not exactly easy to hide. It kicked all the parts it could attempting to "unstick" the missing ball and this happened 3 times when you pressed start. Then the game fired up normally and worked.
Other than some normal maintenance and replacing the very worn balls, that was all that was wrong with mine when I picked it up.
Well Friday with a buddy we tracked down and fixed the error and I made a short video if anyone is interested in what was wrong, and how it was fixed.
Enjoy.