If you're good with DC motors, it can't hurt to take it apart and clean it with some electrical contact cleaner. That said, the brushes are probably worn. They're not super-common failure items, so a junkyard take out wouldn't be unreasonable. If you can find an old-school electrical rebuilder in Raleigh, you might just have them put a new set of brushes in. Check out the service manual for info on removal...
www.infinitiservicemanual.com
I'd take care of this soon. Having the fan on without it moving air is a quick way to burn out the fan amplifier.
Good luck!
Heath