Well, I couldn't quite figure out my MB factory manual instructions but I decided to just start fidgeting around anyway. All I would do was to pump with the vaccum tester to around 20 or so, then push the pin in to see how far the pressure dropped.
1st I wanted to make sure the reservoir and vacuum line from the reservoir were OK so I started with those: they held pressure fine.
Then I started with the Green and Yellow line going from the engine compartment into the cabin. It held pressure fine.
then I went to the Red and Yellow: nope, would not hold pressure. So I tested the line going towards the driver's back seat, it was OK. Then I tested the one going to the passenger's side over the transmission hump: no, would not hold pressure. I replaced the line but it still would not hold so I continued on the passenger side: the one going to the front door was fine, the one going to the back door was fine, it was the one going back to the fuel filler door and rear door (I've got a wagon) that was leaking. I had to remove the B Pillar and carpeting over the rear wheel, just in front of the jack and 1st aid kit compartment. There was a 3-way splitting the one into two: 1 to the gas cap door and 1 to the rear door lock (it actually goes up the B pillar and under the headliner to the rear of the car. The gas cap line was leaking, the rear door was not. I simply plugged off the fuel filler door line to remove it from the circuit (I don't care if my fuel filler door locks or not).
So far, all 5 doors lock and unlock even after the car sits for up to 45 minutes. Time will tell if I've taken care of everything or not but so far I'm pleased. hope this is helpful to somebody! My experience is that you've just got to chase down the leak until you're to the end of the circuit....