I called the 1-800 number for Fantastic Fan, told them my problem (motor just whirrs away without lifting lid) and they said immediately that they've had this before, the motor is shot, and they would send me a replacement right away. They said it's simple to replace - 2 screws, two wire connectors. I'm supposed to receive it next week. Friendly and speedy service.
I now have to confirm with my dealer that my doing the install (instead of a RV repair place) won't mess with my AS warranty on the fan going forward.
Will keep you posted.
2016 Flying Cloud 25 FB Twin
2002 GMC 2500HD SLT Duramax