After playing the game for awhile the flippers will sometimes stop responding. It can vary between doing it pretty quick after starting a game or it can work just fine for many games before it happens. Sometimes if I turn the game off and back on they will work again but more often I have to put it in diagnostic mode then they will start back up again and you can go back to playing it.

The flipper enable relay at K1 is a 4P, 40 ohm, 6 volt relay. It connects through transistor Q67 (2N4401) and a 7402 at U50 and a 7406 at U56, and ultimately the 6821 PIA at U10. Checking the transistor on the board with my DMM it seems OK. Which component would be most likely to cause such an intermittent problem?

Thanks for the advice, that gives me some things I will check out. If it is a switch problem, wouldn't it just affect whichever side the bad switch is on?