So every few games, the ball will get stuck under the skull. There is a bit if wear on the back edge of the hole the drop target raises through. So when the drop target is down, the ball can get stuck on the back edge of the hole and on top of the recessed drop target. Of course this happens mostly when I am having a killer game. I generally can't even rock it loose- I have to wait for the machine to search for balls, which will raise the drop target knocking it loose.
Any suggestions?