This is an exchange on a Corvette newsgroup:
********************************************************************* > Just diagnosed, oil has migrated into the cooling system. > > 62,000 miles > > Requires engine replacement. > >*** reply *** Actually it's not the same engine but it does share a similar block, may even be the same block now. To answer your question, yes, there are times during the casting process that porosity can occur. Many reasons, cold mould, incorrect melt temperature, poor core material adhesion, impure metal, impure core sand or mix, bad wax, missing glue in core buildup, slow pour, vent obstruction, sprue restriction, improper riser heights, cold shut, and core shift plus a few I forgot. Bound to happen in mass production from time to time and I've seen 2 in my life time of which one was in cast iron block the other in an '04 LS1. The LS1 is owned by a retired employee of GM from the foundry that cast the block. How sad is that?
By the way the LS2 started out life as a truck block.