I recently had mine rebuilt and had the same symptoms as mentioned above. Sent it back and the tech, a local Seattle guy, went through it again and said it ran for a week on his bench. Set it up on my bench with a power supply and it ran for about a day and then stopped. Decided to take things into my own hands so removed the rear cover to watch the rewind process. All appeared good so I decided to try one last "fix" suggested by a friend who has several antique clocks (and BMWs). He has been using the 10-60 M spec Castrol motor on his clocks and said it was the one oil he has found that doesn't get gummy or thick with time.
Voila, the clock has been running for two weeks and after several tweaks to the speed adjuster on the back it now stays within about a minute per 24 hours. I'll be reassembling the dash next week so I hope it's fixed for good.