Hi
I had a similar problem where when the ball went into the Subway sometimes the game would sit there and hunt for the ball. After alot of messing around, it turned out that there is a little micro-switch that sits at the lock point in the Subway that is fixed by two very small bolts. In my case the game had left the factory with only one bolt. Meaning, the micro-switch would move randomly and sometimes not trigger when a ball went there. I put the missing little bolt in to secure it and all fixed. Have a good look at that micro-switch.