126 vacuum lock problem
 

I have a problem with the vacuum operated central locking system on my 86 500SE euro with 250k on the clock. when the drivers door is locked the system does not activate and only the drivers door manually locks. When the passenger door is locked the pump activates but it only locks the trunk and the fuel filler door, the rear and driver's side doors must still be locked manually. Once activated the pump continues to run until it times out after about 15 seconds or so. I figure there must be a leak somewhere but I have no idea where to start looking. The pump itself looks fine (a little loud though). Anyone able to save my ass on this one?

Sounds like a lock switch problem and some vacuum leaks. Just got to locate them. Likely a door element.