I'm of the opinion that if you have 300k on the head without issue, the chances of an overheat causing problems are minimal. I am also of the opinion that most are failed headgaskets misdiagnosed as cracked heads.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42