Windshield wiper transmission [attached to motor] is a "steel" worm gear [screw] and a "plastic" worm wheel 3" diameter. Steel strips plastic teeth. It takes more time to remove all the plastic cladding than to dissamble the wiper assembly for inspection, cleaning & lubing.

Although mine worked with hand movement, my inde commented that when it's installed, the windshield's resistance would be enough to prevent proper operation from a bad worm wheel or motor. Slow movement indicates bad motor.

See photo in this thread
http://www.peachparts.com/shopforum/showthread.php?t=168979

More info in this thread
http://www.peachparts.com/shopforum/showthread.php?t=66429

Most photos & threads are for "e" series, but I suspect your "c" is very similar.

Bob