W123 Dreaded Vacuum Leak
 

18 years ago I replaced all door vacuum actuators and the primary in the drivers door, plus the gas flap and trunk actuators . Recently a vacuum leak has arisen that allows the locking system to only function occasionally. The leak can be heard behind the instrument cluster, so I replaced the check valve and tested the rubber connections, but the leak still persists. Has this ever happened to anyone?

May be to do with the swich to higher and lower the head lights . Or even the controls for heater flaps . You need a mitevac to check out all the small bore vac hoses .Any leak in the vac system will cause your problem .

If you can hear the leak and trace it to a particular area you are well along to fixing the problem. Just think about the leaks you can't hear or are in remote locations such as that tube that feeds the gas tank fill lid. Dig into the instrument panel and you will find it.

if all of the vacuum functions are affected , look to the vacuum canister and conenctions there. If localized look to the connections just before the problem area, and for sure check the diverter in the drivers door, the aftermarkets are prone to failure