If you have not already, you need to go through and tighten all the switch stacks, clean/adjust switches as needed, dis assemble, clean/lube all step units and score reels, and chk the coin switches.
remove bulbs, clean sockets.
go back to that coil without the bug, and see if you knocked something outa whack.
got the schematic? get one from PBR.
cant really tell from pics, but looks like a fair amount of rust inside?
it cud use a good cleaning.