Did you try using you mity vac to pull vac directly to the vac reservoir. I know it will takes a lot of pumping, but maybe the reservoir is leaking. I guess an easier way to test that would be to pull the connector off the res. and plug it. Then tee in your mity vac into the door lock system like you had before and start the car and see what it read. If it's still 4-5" then the leak is somewhere else. If it goes up to 21" then it's the reservoir.

__________________