You mentioned that there is no vacuam leak, but the rest of your paragraph STRONGLY suggests that you do have a vacuam leak. Have you put a vacuam guage on to verify that there is no leak?
If you haven't used a test guage yet, I believe that you need to do that. If the vacuam is low, say 15" or less at idle. You need to start the search for your vacuam leak. I expect that the leak is significant if it is effecting your transmission modulator.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in