Sometimes they stick, too.
Listen to the man, it probably is the final stage resistor. Guess I have done this three times, now.
But on two occasions, the fan just "stuck" and when I opened up the plenum (search online, it ain't too easy, you have to remove the windshield wipers and the plastic cowl cover) and then just "spun" the fan by hand, it worked fine after that.
I think the carbon brushes can get stuck to the armature after a heavy rain. Or it could be a sign the fan is about to fail.
It is not too hard to replace. The hardest part is taking off the wipers, plastic cowl cover, etc.