None of the Vacuum-locks in my w123s are currently working, but so far they haven't randomly operated while my car was unattended. As for disabling them, First I disconnected and plugged the underhood vacuum supply line on both my 240Ds because a leak somewhere in the sysyem was preventing the diesel shut-off unless I locked the driver's lock button before exiting the car.
Next, on the 240D I drive the most, I've been pulling the door-panels (front passenger and both rear) to unhook and move/tie out of the way the actuating rod from the vacuum motors. These rods actually have a flip-flop spring-link that's supposed to allow overriding the vacuum motor, but in reality, the flip-flop link is so stiff that I'm constantly struggling against whatever position the vacuum motor happens to be in. Since the vacuum motor still wants to pull or push on the lock button, I got tired of fighting with it everytime I wanted to manually lock or unlock the car. Now, with the rods disconnected, the lock buttons all move very nice and easy.
For the purists, it's not a big deal to go back later and reconnect the rods if you wish to spend the time, sort out the leaky locks and make them whole again.

Happy Motoring, Mark

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DrDKW