Ok,

My car had (1995 e320) had same lock symptoms on Driver door. The lock tab would go down, but the door would not actually be locked. All other doors would lock and unlock as expected)

I have removed the latch assembly from the door. I see the same sheet metal tab was bent as shown in the image from @williammajor (looks like it is supposed to index into the notch on the mating sheet metal part). I used needle nose pliers to bend it back to where it indexes squarely in the mating part's notch. Now, I cannot - with my fingers (w/o fear of applying so much force that the other sheet metal bracket might bend) toggle the lock linkages to the locked position. Is that normal? I would think that the toggling of the latch to lock/unlock positions should be easily achieved. Does the pneumatic actuator really apply an incredible amount of force? Or do i have binding somewhere else in the latch?

I do not want to put this all back in the door without some indication that the latch is "normal/good." My gut tells my my latch is bound up and probably needs to be replaced. I would like to get my car back together however.