Well, I think I know what I would do Mike. I would have it repaired locally.
Its probably out of warrantee by now and as the movement can be worked on by any competent watch repairer, I think I would opt for a local fix. Take it to someone you trust with watches and who is familiar with the 7750. That should be just about any good watchmaker.

If getting the movement out is a fairly straight forward job, then I can't see any reason to send it back to Germany.
If its ticking over by time, from date to date, then it is probably something on the actuator side. If I remember correctly the last time I saw one working out of the case, it has separate actuators to scroll the dates and days. Perhaps the date side is stuck, broken or bent which is not affecting the day advance.
Just a thought.