300TD Ongoing Vacuum Problems

[benchracer]

In checking vacuum problems related to door locks, I've managed to narrow interior vacuum leak to fuel door or rear hatch, haven't had time to finish that one.
I've also checked the vacuum lines in the engine compartment and have noticed something unusual. I connected my vacuum tester to one of the "T" fittings off the main vacuum line going to the brake booster. I plugged the other "T" fitting. The vacuum, at idle, would creep upward to the 20hg mark and then drop down below 13hg before creeping back up to 20 again. This up and down measurement is continuous. This seems to point to the vacuum pump itself. Can this be rebuilt? Does the pump need to be removed from the engine? It looks like the plate at the front can be removed by taking out the screws around the perimeter. I'm also wondering if this can be the cause of recent transmission problems > when I floor the accelerator to engage passing gear, the tranny takes several seconds (if at all) to drop into passing gear.