Then the lock actuator is working. The possibilities:

A)Broken nipple at the pump

B)Leak to the front door

C)Vacuum motor broken latch/leaking

I would swap a vacuum line at the pump with another door to qualify the vacuum to the door. Also, if the vacuum connection is wobbly, nipple is broken. The problem is right there.

Here is some food for thought...Post 12

A wonderful article about Close Assist Pump by Brett - Mercedes-Benz Forum

MArtin