Here is what happened to mine, and probably most of you people as well...
Notice the right side of the gear that has a chunk melted/ground out of it.
And here is a way to fix it...
See those two screws holding the bas of the motor to the frame? Get some washers and place them between the motor and the frame, putting the screws through them. This will lift the motor up, closer to the "not-so-eaten" part of the gear. I will be trying my new fix out soon.
As you can see, by performing the first fix as stated by DJBillyHoe and mklarko, you are not really moving the worm gear closer to the gear, you are simply moving it to another section of the gear. My fix does essentially the same thing. I'm just moving the motor, as opposed to tilting the motor.
I'll keep you posted if my fix works.