The music box in my German “Regula” cuckoo (works further marked “E. Schmeckenbecher”) will not consistently play. I bought the clock at a garage sale. Although it was still in its factory packing I found the works filthy. Once cleaned up and oiled the clock ran, kept good time, and cuckoo-ed on cue. But the music box did not. All the linkages are in place, but the box won’t play unless (at the top of the hour) I lift the weight slightly and then reapply tension, then it plays. In ‘monkeying’ with the clock, including experimenting with a lighter weight on the music box, I can sometimes get it to work as intended for a few rotations, but then it slips back to not playing unless I lift & release the tension on the chain. I can’t see any obvious fault that is causing the resistance. Thoughts?