Good advice. I learned quickly that I cannot lock the car immediately after unlocking - I have to wait until the problem pump shuts off. I feel fortunate that (knock on wood) the vacuum system on this car is still pretty good. A lot of 107's have problems because the vacuum system deteriorates and performs like a set of leaky bagpipes - too much air and plenty of noise. I've heard that I could get into the pump and check to see if a certain gear/shaft is frozen up, preventing mechanical shut-off, but that sounds like something best left to a knowledgeable mechanic.
If anyone on the forum has delved into the vaccum pump and has a photo or two, please send it on. Thanks.