Turns out that little cheapo amazon leak detector has given me a clue on this rabbit trail. I charged the A/C just enough to get the compressor to kick on. The leak detector detected no refrigerant near the valves, nothing at the compressor, or drier. I was doubtful the thing was effective. I ran the thing in the cabin, and then it started clicking like mad. I positioned the detector at the vents, and it signaled a consistent and traceable leak. I am surprised that a cheapo detector like this could be so helpful. I am taking the Van to the mechanic tomorrow to extract all the AC. I will take the evaporator out and inspect it for leaks. Hopefully I can trace down the leak and eliminate it.
Is it worth it to replace other seals in the AC system? Ebay has cheap compressor shaft seal and o-rings. Are things like that worth replacing while the AC system is empty? I DO plan to keep this van a long time, since they are known to run forever. AC is one luxury I can't live without. I just don't know if the oem seals are better than cheapo replacements.