I get the feeling that "head gasket" is a much more severe problems for Cadillacs with Northstar than what is being let on. In my thread I am awaiting a new head gasket on a 2001 and the failure mode was equivalent and things done to fix equivalent to this story. In this story on the 99 Seville, by running the engine now without getting a proper repair I thinkhis engine may be toasted. Car mechanics I am told do not like to work on this engine because it is very hard to fix (note that no action was taken for a long time by his mechanic). Perhaps a simple check to see white or gray smoke coming out of the exhaust (and mysterious loss of coolant) should be the first thing mechanics look at on them not the last!!