1981 300D

My locking system wasn't working at all...even with the engine running.

I've troubleshooted the door lock vacuum system and this is what I've found:

Lines and fittings are OK
Trunk actuator OK
Gas tank lock actuator OK
Vacuum reservoir OK
Vacuum switch in driver's door OK

Actuators in RF, RR, RL doors had cracks in the exterior rubber boot. I replaced them with fingers donated by a latex glove, glue and sewing thread. They won't hold vacuum too long but I went ahead and installed them to check. The locks are now working but with the engine running. A few seconds after is turned off...the locks are inoperative.

So...what are my alternatives to fix/replace those actuators? ************************ lists a kit @ 6 bucks each to fix them but they say that 4 of these are required.

One interesting thing happened. Before playing with the lock system...the cruise control was totally inoperative....however, when I replaced the lock actuators with the temporary repair...the cruise control began to work partially. It would accelerate the car when the lever is pushed up but it wouldn't keep the selected speed. I thought tha locking system was isolated from the rest of the vacuum system by means of a check valve at the firewall or something to that effect. Any clues??

Thank you.