First off, I'd like to apologize for not introducing myself. I've already solicited your help with a couple of dumb questions (thanks!), and I'm sure to have a few more in the future, so...

My name is Andy. I played my share of pinball growing up, but never really thought at all about how they worked until recently. I picked up a Dr. Dude machine (the subject of aforementioned dumb questions) and used posts on this forum to get it up and running again. It's been a real pleasure working on it, and even more fun now that I can play it.

Today it developed a drop target issue. 3 of the 4 drop targets fall when hit, signaling with a noise and light that they've registered. The last one will fall (slowly), but it's not registering the hit, so all four targets remain down and don't reset until the ball is lost, at which point they all pop up fine.

I took the target out and cleaned it and now it is sliding well, but still not registering when hit. I used a dry Q-tip to gently clean the horseshoe-shaped circuit that the target slides through, but didn't want to go too crazy on it and mess it up.

Is the horseshoe-shaped circuit likely the source of my woes? Any advice on how to clean it properly? Any other ideas?