Jim,
I read your post. If your oil cooler ring is doing this, it could have your
symptoms. Van heats up, oil cooler ring expands, and no leak. Cools off, ring
shrinks, leaks.   My 86 Westy did this, and I ignored the problem. My mech even
had told me that the ring was leaking and I would need to replace because it
could go catastrophically. Well, I didn't do it, and on a trip to San Luis
Obispo from Orange County, the ring went catastrophically and all my oil drained
out onto the road in about a minute Thank goodness I was close to Gowesty.
Short answer - if it's your oil cooler ring, don't hesitate to fix.
Dixon