83 300SD door locks

hi all,

i am having a problem with my door locks on my 83 300SD. if i turn the key in the driver's side door only the drivers door will lock, but nothing else locks (doors,trunk, gas door). if i try to push down on any of the other door knobs they pop right back up (pressure is poping them back up). after about a min the pressure is gone and i can push down the remaining door knobs. the doors unlock just fine. i have read several posts on here regarding the vacuum operated door locks, but didn't find one about this particular problem. so my question is: is there a problem with the drivers door actuator (maybe a sticking contact that makes the pump think the doors are being unlocked when they are actually supposed to be locking). or could it be a problem with the pump itself? if anyone had this same problem or can give advice i would greatly appreciate it.

E.