you need at least a new wiper motor, there is a plastic gear inside the motor that a worm gear moves.. the worm gear breaks and then the plastic gear strips in one spot. id recommend doing everything but its pretty pricey.
at least replace the motor and linkage (linkage isnt very much).. the gearing is pretty expensive, you can probably hold off on that, but should really lube the gearing up, like in that link that is posted up.