The damage was traced to the black gasket. It was sold to me as new from my local parts store. It's a Felpro that was discontinued many years ago. Note the water passage at the very ends. They are very thin. That meant there wasn't enough material to keep from blowing out. When it blew, all of the water in the cooling system, 6 GALLONS, went into the crankcase. Not good. The Mr. Gasket product replaced it. You can see how much more material there is at the point of failure. Grr.