You have a vac leak on the unlock side it sounds like.

Here is a good thread with the W123 vac lock diagram.

W123 Vacuum InterLock Diagram

You will need a Mity-Vac to chase down each side of the system.

You could have a leak in the Climate control system, Green line
Or a leak in the engine shut down side, the brown line.

From what you are saying it is probably one of the door, fuel door or trunk actuators leaking.
Also a possibility a yellow plastic line or one of the short rubber hose connectors are leaking.

Some times the plastic line going into the doors from the body will crack over time from heat and bending,


Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works