Quoted from Gotfrogs:
I have only had my machine a few days and have noticed that often times only one or two balls drop from the couch when I get couch MB. The bracket seems to be pointed slightly inward towards the coil piston. Should I try and bend this metal piece outward?
I don't think so. See if you can figure out how the balls are getting stuck first. For Couch MB, the game will dump the balls slowly, but it's not going to let anything hang up in the lock at that time. So I'd wager that they're hanging up somewhere.
Either there's a hangup, or there's a switch problem.
(I guess it's possible that it's pinching there, but if *some* of the balls are coming out of the couch, that wouldn't be my first guess.)
I'd also take the couch apart. There's a "fix" for a weak part on the couch (535-9307-00) that may be relevant. I had my game for a few years and discovered, when I pulled the mini-playfield to clean it, it had been broken (and apparently working) the whole time. This might be your issue -- in this case, the solenoid might be having trouble pulling in because the coil stop has fallen off.