Leaf switches very, very rarely actually "go bad". Usually they just get dirty. To clean them, just put a scrap of paper between the contacts, push them together to put pressure on the paper, and slide the paper out. Should get a little dark line of crud on the paper.
I've seen end of stroke switches in pinball machines go bad though - they start to get real pitted and arc, but those are high current.
Usually, when a button doesn't work like that, it's not the switch itself, it's the wiring, or the connector pins on the board - especially on Wiliams games. Usually, there is a cold solder joint on the connector on the interface board. Or, one of the buffer chips has a bad gate. Easy enough to check though - just put a screwdriver or other metal object across the side of the switch, joining the two blades together, bypassing the contacts. If that works, then the contacts are dirty. If it doesn't, then you have some other problem.
-Ian