It's the "V" word Vacum. You have a leak, maybe the line or maybe the diaphram in the lock actuators. Plug off the line that goes to the fuel door first (in trunk @ "Y" branch) common leaking problem. Do you own a miti-vac? After that you will need to isolate each door (use golf tees to plug lines) to find where your leak is. There is volumes of "Lock Leak" information on the search feature.
SDL's hardly ever need repair so this is probably the only DIY job you will have to do on this car
