Well, I'm still at this. Tried on and off over the winter. Spent most of this morning friggin' with it too. It is jammed so tight, trying to turn the striker seems to be impossible too. Not sure where to go with it now.
Try putting a jack under the frame rail about half way between the hinge and striker below the door and lift the car a little at a time, try the door as you incrementally jack the car up and see if it lets go. I have seen some cars that (mostly convertibles) "settle" (or sag a bit) between the front and rear suspension.
