Nelson,
Using any of the available smoke EVAP testing machines ( the more you spend the better they work) simply go to your initial source of vacuum for the combined headlight / wiper system and hook the machine up to that hose and if needed, use vice grips or a clamp to shunt out the working headlight system although at first I would check all as multiple small leaks spell trouble for that darn door.
The machine pushes the smoke through the system.
Then just look for the escaping smoke and there is your problem.
If you find no leaks, first remember to look in the passenger compartment, as that is often the culprit, i.e. headlight switch, overrides etc.
If no leaks are found, start at the manifold and work outwards through each device both in the engine and passenger compartments, until you again find the culprit.
Make sure your hard to find a replacement door mechanism is not binding.
Also double check that the hoses are properly connected. There was a long production run of wiper control valves that had the colored dots on the wrong ports causing the system to work against itself.
Patience and starting at the beginning always seems to find the problem.
Or send it up and we will take care of it.
Go get em!
Marty