I would pull the carpets and then look under the plastic cover running down the outside of the footwell. All the vac lines for the door locks are there. Thats usually where I start troubleshooting the door lock vac. You'll find two 3 way connectors, one unlock(yellow/green) and one lock(yellow/red). Here is where each line goes for both sets of lines.
1. Master door lock switch in the drivers door
2. Driver's rear actuator.
3. Passenger side and trunk.

On the passenger's side under the same plastic cover you'll find two 4 way connectors. Here is where the lines goes.
1. Vac coming from the driver's side
2. Passenger front door.
3. Passenger rear door.
4. Trunk and fuel door lock.

Here are a couple pics of the lines in the footwells.
1. Driver's side.
2. Passenger side.

Test each line by pulling vac on it, and work your way through the system This will tell you which actuators are leaking. Test both the lock and unlock systems. As one side can leak and the other won't.

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