CM 871 head gasket up date

[heavy hauler]

Quick reminder for all... my head gasket let go on the front driver sided water jacket, external leak. The head came back from the machine shop, pressure tested, valves cleaned and seated, and a fresh surface. they said there was nothing alarming about the head, also gave them the gasket for further inspection, also saw nothing else other then the fail point. I had them check the deck, along with liner heights. truck has 800k in it. I would assume factory engine, I bought it used. cylinder walls are perfect , nice hash marks all even along with NO carbon built at the tops. the truck has been Demandated for at least the 4 years i've had it.

Still just unsure why the head gasket (OEM Cummings) replacement only latest 2.5 years , 175,000 miles.