I replaced a head gasket that was beginning to fail, but the head was fine. Does the failure of a headgasket impact the potential for a cracked head? How so?[/QUOTE]

Logic that the leaking combuston gasses might form an air pocket by displacing the lower pressure coolant flow in a given area resulting in a hot spot. Repeated many times could cause a crack by the difference in expansion and contraction of that portion of the casting. Most the time fortunatly this does not happen to the extent of damaging the cast iron head.