OK, I'm really going to flame folks here and expect to be deluged with hate
mail.

The guy behind the VW parts counter in Wichita said he was the rep who went
to Germany for VW Vanagon training for the USA.

He mentioned that you MUST use VW coolant as the sensors were calibrated
for it. He said even the Fuel Injection could be screwed up if I used
something else for coolant. Coolant/water ratio was also imporant.
Look, it's an extra $10.00 per gallon. How much do you use? An extra $10
per year seems a good investment if it just might help solve some of my
engine/cooling problems.
He said the Vanagons in Germany did not have the head gasket problems we
did. Is it cooling related? Cooldown after highway related? Whatever.
Trying to save $10 by buying green prestone or whatever seems like nonsense.