Oh, man! I was playing my Junk Yard tonight and I THINK I had the same thing to happen. When the ball goes around the magic bus loop my switch has suddenly stopped registering and the ball ALWAYS goes to the right flipper. Plus, it does not reward me with a piece of junk. Looks like I'll be changing out a switch too, and I sure hope I don't have the same problems you have. If I do, I'll be in the same boat because I won't know what to do then! I wish you the best. I'll be watching this thread to see if anyone gives a solution. Good luck!
Mike