Search for Junkman's headlight gear replacement thread. That will at least give you a very good overview of the parts you will be dealing with. I'm thinking more than likely one of your bumper stops is chewed up, allowing the arm to pass it. This happened on my car after I did the headlight motor gear repair. The glue popped on the motor housing which allowed the arm and assembly to shimmy to the side, bypassing the bumper stop. Since then I've gotten some new stops and resealed the housings and all is well. Hope that helps some.
I'm sure someone will get on here with some links and/or pictures.