YoungBenz: Obviously there is a vacuum leak somewhere. Do you have a Mitivac? You need to find out if your system can store vacuum over night, or if the leak is constant. It sounds like the rubber nipple on the rear door lock actuators have torn, and they allow air to escape as they flex (when they are opening or closing). If you don't know what I'm talking about, open up one of your doors and remove one of the lock actuators. I don't know where to get those nipples besides from a dealer, so I just delete a vacuum lock actuator once it needs a new nipple. Once they're all deleted, I'll install electric locks!

sclancy: the driver and passenger lock actuators, which control the lock/unlock of the car's system, have one tube for lock and one tube for unlock. Maybe the lock tube on your front driver lock actuator is disconnected or cracked or something?

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'82 300TD
'77 6.9
'75 280S
'74 280
'87 Porsche 944 turbo