Tom,

The ones I've done it is gunked up motors. Typically water gets to the
shaft at the bearings top and bottom.  Disassemble the motor, clean up
the shaft and bearings and reinstall.

This is a job to get the corroded motor apart and clean and then
reinstall in a timely manneer.  I have one extra motor.  I install it
wherever, since they interchange left and right, then at my leiesure I
repair the gunked up one for the next time.

As of yesterday I have my left door to do, this is the fourth one in
four years, so about 18 months and they're ready to redo.  I'll still
thinking on a way to extend the Mean time between failures-- So any
ideas I'm listening.

Sincererly,

Mark Keller
91 Carat