OK... well, after all my flailing failed me, I grudgingly resorted, as a very last resort, to rational thinking.
I started at my micron gauge, and tried to pull a vacuum on just the micron gauge. The readings were dishearteningly high, so I checked the fillings for tightness. Everything was OK. The gauge has a battery life graph and it looked fine, so I pulled out the 9v battery and measured it... almost a volt low. I also looked into the end of the micron gauge's fitting and saw more than a little bit of oil, so I bought a new 9v battery and some 99% isopropyl alcohol and filled the gauges thermistor cavity with alcohol, let it soak, and shook it as best I could and emptied the alcohol. I repeated this - three times, and let it dry over night.
Then I pulled a vacuum on the whole unit and got down into the few hundreds of microns range (a big improvement), and capped the heat pump off. The morning after that, I hooked up my flared copper vacuum tube (I use this instead of expensive vacuum hose) to the vacuum pump, and I pumped down the line, then I opened the valve to the heat pump that had been pumped the night before, and there was no jump in the vacuum gauge, so I think that the vacuum is good.
All of which makes me question my previous results with the air compressor, etc.
I think that I may have a questionable Schrader valve core in the heat pump. This will be easy to replace.
Also, the refrigerant valve that connects to the 1/2" line was persistently leaky, but now it doesn't seem to be. I'm really not happy with this possible answer, but it may be that all the working, opening & closing, had the effect of re-seating an O-ring. Whatever it was, it does seem to be holding.
Darn, I was looking forward to doing randen's flame test, too.
Through all of this, I have not been using new, fresh vacuum pump oil, so new oil should make a big difference.
Thanks for the suggestions!
Best,
-AC