The fix is only temporary, But, a good one.
Remove motor. disassemble, Clean the grease out of the brush area, and it will probably work if you get it back together. Them little brushes are a bit of a challenge. Doable but a challenge.
It will last another 400-500 hours before you have to do it again.
I've got an RV-6A and at 501 hours it stopped working. It gave me a warning at about 480 hours, But, I ignored it. Not anymore. Cleaned and it worked/works fine.
Or buy the better motor from I don't remember where, But, it's on the forum here somewhere.
Art