Ok guys, this one has me puzzled (they all do as I'm still new at this!). Sometimes and not every time, when playing, a ball goes in the lock trough that isn't registered and the machine goes into hunt mode looking for it only to kick it out without registering the lock. I've ran a switch test and all switches test normally as working.

Any ideas?

Also, are all games of this period clear coated?

Yeah, I've used the balls in test mode to test the switches and they all test normally. This was after first powering it up too.