The link rod which connects from the push/pull locking knob to the door latch, runs through a plastic guide. The plastic guide is in approximate center of the door, and is U shaped. The link rod snaps into the plastic guide. If the link rod comes out of the guide, the link rod will flex enough that it won't unlock the latch. You may be able to roll the window down and look for the rod. I don't remember the exact details, but this is how I opened the stuck rear door on my brother-in-laws 745.

If you take the door panel off the working rear door and see what I am writing about. The plastic clips at the bottom of the door panel can't be removed with the door in place.

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john