I agree, sounds more like the roll pin has slipped from it's bore. Also sounds like it is intact and catching on something, preventing the key from returning to the upright position. You will have to remove the outside handle to fix. I think the 124 is very similar to the 126, find the plug on the door jamb (previously mentioned), remove it and you should see a large phillips head screw. Remove the screw, now you can gently slide (might require a little force) the handle toward the front of the car. Once the rear has disengaged, it will pull out.
Normally at this point you would need to turn the key to free the hand from the door. Maybe it is stuck in the proper position. Once the rear is free of the door, slide toward the rear to disengage the front.
Installation is reversed.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.