I had exactly the same symptoms on my '86 Syncro
Westy.  A fellow Vanagon owner at my previous employer
smiledas I told him about the problem.  Then he said
convincingly: "It's the seal inside/underneath the
heat exchanger.  Pull off the oil filter and then pull
off that water-to-oil water heat exchanger that the
oil filter is mounted to.  Replace the seal
inside/underneath and your problems will be gone!"
Guess what?  He was 100% right!  Best of luck.

Mike Conlon
1986 Sycnro Westy "Fritz"
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