I have examined a number of failed head gaskets and the problem I have seen is acidic coolant corrosion of the metallic portion of the gasket. If people would simply change the coolant at less than 2 year periods, failure of the head gasket would be reduced.
Another problem (more in the past than now), was the interface between the aluminum head and iron blocks. The coefficient of expansion between the two materials was different and caused problems with the gasket.
One of the cures for the older S-10's (of which I am very familiar) was to place an additional copper gasket between the aluminum head and the lower block gasket, which meant better heat dispersion for the aluminum head and the lower steel gasket.
[ November 29, 2002, 11:27 AM: Message edited by: MolaKule ]