Quoted from TicTacSeth:Getting under the playfield, I see the top gear slips because one of the teeth is either gone or bent, so it doesn’t catch unless I push the rotation.
Mine is damaged in the same way. I've thought about trying to tighten it slightly with a heavy zip tie across the two shafts. If I could find gears, I would rebuild. Barring that, there was a way that I thought of that might work or be a total disaster. Put a dab of JB Weld on it and let the remaining teeth "cut" grooves in it. Rotate it away from the worn area with jb weld and let it harden into "new teeth."
Now, this is just a crazy idea I had while looking at one that would probably be replaced with a Marco unit if I route it, so don't try it unless you are also willing to toss the whole unit if it goes bad.