Sounds like the bolt might have just come loose. Check that first; Pop off the black cap at the base of the wiper arm, and see if it's loose at all. If so, make sure the wiper is in the correct placement, switch position off, and tighten it up. It's rare for the wiper trans or motor to go out of these, most of the time it's just the loose bolts or the "tab" you speak of.
Good luck.