Howdy all.
I have a scanned image of the oil passage from a Isuzu manual, but I can't post it here. I can e-mail it to anyone who wants it.
My best guess is a leaking regulator valve. The valve is slow to close, and doesn't seat all the way, so when shut down long enough, the oil drains back to the sump. Good chance there is some crap in the valve.
Just my 2ó.
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