You need to redefine overall vacuum system.
The door locks including trunk and gas flap are just one of the various vacuum operated systems on your car. If you still don't hold vacuum then you still have a leak. The vacuum locks in the trunk are often disconnected and plugged when that gets the rest of the system working.
Vacuum losses in other systems can cause the door locks problems. Lots of info in the archives.
Bosch Master, ASE Master, L1
33 years MB technician