Hi Bernard,
I have nowhere near the experience with cuckoo clocks that William does, you say the clock is running fine outside of the case but then stopping on the bird exiting the case, have you checked the rod from the bird to the door? I had one like this and in certain situations the rod would twist enough to stop the door closing, almost locking it into position. It certainly doesn’t sound like a movement issue if it works ok out of the case so as William suggests, check where the case parts are connecting, as i am sure you already know it only takes a rod to be slightly bent the wrong way to stop these things. Along with 400 day clocks, cuckoo clocks are my worst nightmare so I send all my customers with these to William 
