I had this happen on a game with a new power supply once (TFTC). The game would play for hours (sometimes days) on location and just crash for no reason at all. It was so annoying. Every socket and power test point was checked and all were fine and the test points never fluctuated thought the months that the game was on location. It turned out to be a flakey EPROM. I burned new ones and it solved the issues. I would at least look at replacing the game and sound EPROMS before you buy a new MPU. They are not that expensive.

Possibly. But I would suggest buying them from someone on Pinside that specializes in such things. I don't stock these EPROMS.