Every movement or maker has its weak point. With Hermle it was the chime locking cam. It was used on all of the chiming movements. The above photo shows the 1161 grandfather unit and the below on the 341 series.
The weak part of the cam is the pin itself which provides the lock. It breaks a lot. Shown in the left photo is the front and back of the old style. One has the pin intact and the other the pin broken off. Also shown is the new style solid locking cam which can never break. Another improvement is the fact the arbor it is on is larger to not only provide more strength but also to lock down better. The cam attaches by means of an Allen wrench instead of the small set screw to give much better tightening.
It is important to note that both the cam and the 4th wheel need to be replaced as a pair and Butterworth Clocks has the parts. Also I will note that this improvement has been made by Hermle quite a few years ago, but I still see on the message board questions about how to replace the pin. DO NOT DO THAT! If you are going to repair this do it right and do the job with an improved part. The original was weak and to do a repair is only going to introduce a weaker part yet. It is a disservice to yourself and your customer.
Final thought: If do not have the time to do the job right the first time, how will you find time to redo it a second time?