Owen_Dyneto wrote:
It's happened to me and others, kind of a classic also with Cadillacs sharing the similar vacuum pump system. You're perhaps feeding oil from the crankcase into the intake via a failed check valve on the vacuum pump line. I just pulled the rubber line at the firewall and put a twig into it until I got home and cleaned the check valve.

PS - check valve is on the passenger side of the block, just above the oil pan/block interface, about midships.