It seems very odd that there was no coolant in the oil before you
changed the gasket, and now it's running out of the pan.
Anyhow, here is an idea. If your van has an engine oil cooler in the
radiator, you might want to disconnect the oil cooler lines from the
radiator (Left side/driver's side). Then, add water to the radiator and see
if it runs out of the cooler connectors at the radiator.
Usually when the head gasket leaks coolant, it's into the cylinder, into
the lifter valley, or out of the engine. If it gets into the cylinder, it
usually stays there. It can't get past the rings until the engine is
running. Well,... it can, but not fast enough to see it pour out of the oil
One last test. Apply compressed air to each cylinder with the spark
plugs out. Use a compression tester. Some of these have a 2 piece hose with
a quick coupler. If yours doesn't have one, then spin the gage off and put
an air fitting on it. One by one, apply about 20-30 psi to each cylinder. If
you hear air coming out of the radiator neck, then it's time to pull the
heads, inspect the gaskets, and inspect the cylinder walls for cracks. Of
course, this requires an air compressor and a compression tester. If you
don't have these, then you can't do this test.
That's about it. I'm tapped out of ideas. Perhaps another in the group
may give you some more.