Remove the whole vent frame assembly from the door, if you haven't already. It's held in by a bolt on the bottom of the vertical guidepost and 5 screws (if I remember correctly) around the vent window. Then you can remove the nut, spring and spacing washers on the pivot (don't lose the washers!) I used a Dremel to grind the rivet out of the hinge; you could drill it if you're careful, just don't elongate the hole. I ordered new rivets and a setting tool from ChevyDuty, although once you've flared the rivet you'll probably only get it snug (so it doesn't rattle) with a vise or some other form of press.
