the watch needs to be sent back for another intervention. I suspect the best/most skilled watchmakers are on the production side. Or when they specialise in the movement servicing and are really good, they go independent. In addition, factory service is usually limited to replacement of parts if any, however minimum, wear and tear signs are detected; this may increase the service costs enormously while 'classical' service (cleaning & lubrication) would bring identically functional result. After not the best experience with JLC, Blancpain (in the Switzerland), my first option is a local independent. When receiving the watch, he makes a preliminary diagnosis, witchi and detailed inspection under the microscope, it is always very interesting to see the movement on a 20" screen, lubrication in the stones, on the escapement etc.
Perhaps someone here might suggest a good watchmaker in Germany trained in Lange movements?