Hi Jeff,

I had the same problem last year. The root cause, in my case, was that the plastic cylinder going through the glass had cracked letting water and dirt in and making the shaft seize in the "frame".
After that the motor chewed up the integrated "gearbox" (sorry about my English) so I could hear the motor running and nothing happened.
Off I went to remove my tailgate trim. Then I unbolted the entire wiper assembly from the tailgate.
Once I had separated the motor from the assembly I knocked the shaft which the wiper arm attaches to out with a hammer. It was very badly stuck and the surface was very corroded. Due to this I considered buying a completely new assembly but to save some money I cleaned everything carefully and put the shaft back in with an excess of sticky grease.
Before putting a new motor (approx 100 bucks) to the assembly i connected it to the tailgate and ran it to get it to stop at the correct position (one would assume that it was delivered that way but I wanted to make sure).
Getting everything back was a piece of cake, just make sure you connect everything in the proper resting positions or you will be wiping your license plate (don't know if that could actually happen but I remember I put some thought into it). One year later it still works perfectly.

Good Luck
Johan