If the one door is slow to lock, there are some tests you can perform before even tearing anything apart..

1. Sit in the car, engine off, doors unlocked. Push driver's plunger down and listen to both doors for any hissing noises. You will most likely find it in the door that is slow to lock.

2. With engine running, press driver's lock plunger down and see if it still takes a long time for the other door to lock.

You can remove both door panels and put a vacuum gauge on the elements in the doors and check if either one of those is the source of the leak. The yellow/green line is the unlock side, the yellow/red line is the lock side. In the meantime, if you don't want to diagnose the source of the leak yourself, you can just pop the hood and disable the entire central locking system by plugging the yellow/green and yellow/red lines back by the firewall, where they come out atop the oil filter housing.

The emergency shutoff lever under the hood will look right at you if you're standing on the driver's side of the car looking at the valve cover. It's a piece of throttle linkage with a red label on it marked "STOP". Turn the key off, pop the hood and push this linkage towards the valve cover to kill the engine.

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Regards,
Aaron