TL/DR - I wrote a long version of this story and question below, but realized that the question is fairly simple. On my 87 300TD the rear driver door doesn't open from the outside after the doors have been unlocked. I can open the door from the inside and once it has been opened the door opens as normal from the outside. However once I lock and unlock the doors again I can't open from the outside. Do I need a new door latch mechanism or is there a mitigation I can try here?


Longer version:
On my 87 300TD the rear driver side door would never lock. The door lock would travel down as expected but then slowly rise back up. My assumption was that the actuator had a vacuum leak, but after pulling the door panel and testing the actuator with a mighty-vac that turned out not to be the case.

Upon further inspection I found that the rod connecting the actuator to the door latch was very difficult to move to the locked position, i.e. it would travel part-way rearward then bind on something and never completely lock. So the actuator was trying to push the rod to the lock position but was never actually able to completely lock the door. With the door panel off the rod would actually start to bow outward at the binding point and pop out for the plastic holding clip for the rod.

I found that manually I was able to push the actuator rod to the completely locked position, but it took a lot of pressure to move it past the binding point.

As a next step I decided I would try pulling door latch and see if I could find the binding point. I loosened the three bolts for the door latch mechanism and found that, after loosening the bolts, the rod started to slide to the lock position with ease, i.e. it was no longer binding. I re-tightened the latch bolts and now the door locks and unlocks with the vacuum actuator as expected.

Now I've found that when I lock the door and then unlock it the door remains locked from the outside. I can open the door from the inside, and once it has been opened once I can open and close the door from the outside without issue, but as soon as I lock and unlock the door again I can no longer open from the outside until I open it from the inside.