I got to pop the cap off of this yesterday and yes Kevin you were right on the money: the contacts were too close together, and I actually know why- the ball had managed to get itself in there a couple weeks ago and I had to finnagle stuff around to get it back out. The result in the ball getting in that area bent up the contacts. So, I popped the top, bent the contacts apart CAREFULLY, and I also cleaned the contacts with a business card. Upon putting everything back together, it now only responds when the ball hits it, and only does so ONE TIME.. Joy! When I saw how this part of the game worked, I have to admit I was totally impressed. It is simply amazing how much electrical engineering and related physics go into making a game like this work. Like with a car though, you never really realize that until you "see" what's making the functionality happen right in front of your face.
I also noticed yesterday that when the ball goes up the right side of the playfield and hits the spinner to let the machine know that it should show the letter "R" of Sorcerer as hit/bumped/enabled, it's not doing what it should.. So, you can get the word "SORCERER" lit up 99% but no payoff for getting the last 'R'. I'm pretty sure it's something within the spinner connection, because for every other part of the game display, the light blinks as it should- it just doesn't register that the ball has hit that spot. My daughter's bday is in July and we have a party that weekend (duh), so I think I'm going to WAIT to mess with that. Something about lifting the playfield right now tells me "don't do it".
And in final update news, I found 3 more screws in the cab that should have been in to hold the PCB in place. I also found the eprom that I dropped from the speech card! Amen..
Yup.... and if you haven't taken a good look under the playfield yet..... prepare yourself.

Adjusting the switches is generally a matter of tweaking the leafs one way or another.
Sounds to me like you have one sticking closed when it should release.
Usually (in your case the bumper) you can activate the bumper and while it's stuck you can open or close the leaf switches to figure out which one needs to be adjusted.
Edit: Just looked at your pic again and realized what you were talking about. ( I was thinking about POP bumpers for some reason)
Those bumpers need adjusted from the top side of the playfield. You'll see the leaf switch right behind the rubber. The gap is probably too close. So bending the switch a tad to make the gap between the contacts wider should do it for ya. When the ball hits the rubber, the switch should make contact. When the rubber rebounds due to it's natural elasticity, the switch should open and remain open. The contact could be a bit dirty too from arcing, so try the business card trick and slide it in between the two contacts a couple times.