central locking problem

[tenmaz]

The car is an 87 300 SDL. I'm having problems. The driver door key will not lock or unlock, but if I reach in from the rear door and press button on drivers door with door closed all doors will lock. Passenger door key will lock and unlock,but pressing the button does not work. The trunk key worked both ways until today, now it will not lock. It does not seem to be a vacuum problem. I have had it locked for several days and it will unlock and lock again without running motor. Any details to inspect and repair will be appreciated.