Originally Posted by babymog

Since you have a T124, not a W124, it is under a carpet piece beneath the right rear seat and you will probably have to pull the threshold plate to access it.

Do you hear the pump cycle when you lock and unlock the front doors? It should be a faint compressor noise, hard to hear unless all else is quiet (tip the right rear seat forward to listen).

If not, it could be either the pump, a fuse, or a switch. There is a switch in the actuator in each front door, and one in the hatch, any one of them should run the pump (try all three if you can't hear the pump).

If the pump is running, the next step is to apply vacuum / pressure to the system to see if it is an air leak, which could be any of the (6) actuators or a line/fitting. Open the rear cargo compartment where the jack is stored, you'll find a yellow line leading to a rubber tee. Hook up a vacuum/pressure source at this tee and apply vacuum & pressure, locks should actuate. If there is a leak, you will be able to narrow it down by the three lines which go to: hatch, fuel-door, all doors including vacuum pump.

Common leak areas? None really, but I'd suspect an actuator first, then possibly a line damaged in a door-jamb, last would be the lines in the floor.

Good luck, I'm going through this again also.