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.

I'd probably start by removing the door panel to get a quick look at the mechanisms. Shouldn't take you long. Quick video for the front panel, minus the seat controls:

https://www.youtube.com/watch?v=Z2MGyY89SLw

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1987 300e W124 M103 My baby.

NVM. Read your longer version...

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1987 300e W124 M103 My baby.

It would seem that there is a problem between the actuator rod and the catch coming from the door handle. Have you tried removing the handle to check the catch?

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Don't Chrome them; polish them

Last night i went ahead and pulled the door latch mechanism. It seems like something is sticking in the door latch internals. With the mechanism out of the car I could easily replicate the problem by pushing the latch to the closed position then actuating the lock/unlock lever to replicate locking/unlocking the door. I would then pull the lever that the exterior pulls expecting the door latch to move to the open position. Except that it would not.

I noticed that if I tapped the mechanism on the ground a few times the latch would then release, leading me to believe something is sticking in the latch internals. Maybe old grease gumming up the internals?

I sprayed the mechanism down with brake cleaner for a bit to get the old grease off. After doing this the mechanism started working as expected. I went through the whole routine described above probably 50 times and it worked every time. I sprayed everything with some silicone spray lubricant as well.

Thinking I had solved the problem I went ahead and put the mechanism back in the door, but once I had everything back together it started showing the same behavior and not opening from the outside after locking/unlocking the doors. The only difference is that now if I pull on the door handle repeatedly the latch will eventually release.

So it seems at least part of the problem is that something about its positioning in the door makes it more prone binding/sticking internally.

At this point I'm just going to look into locating a replacement unless someone here has some additional wisdom in what I should try

To close this out I was able to track down a working door latch mechanism and everything works now

I would have like to have figured out what was wrong with the latch, but my lack of free time to fiddle with it outweighs my curiosity.