Not sure how to explain this, so apologies up front. In the process of repairing my vacuum door lock system I ran into an issue with the front passenger door. It's different than the other doors. It appears that MB designed this door system to allow you to open the door while the other doors are in locked mode. I think there is a part missing on mine (maybe a spring). The actuator pushes (unlocks) the door knob (stem) up, but when the actuator pulls (locks) the door knob (stem) stays up. The hardware surrounding the lock mechanism has approximately a 1/2" of play (intentionally); therefore, the stem stays up. I purchased a small pull spring to pull the stem back down, this works pretty well locking and unlocking, except when the passenger opens the door in locked mode. When you pull on the latch there is a quiet clicking sound and the stem stays up until "reset" with system. Is this normal? Also, what is the part that I replaced with a pull spring? Is this available at Mercedessource? Thanks.