my opinion is that when the turbo seal leaks oil into the intake and passes with the hot gases allowed by the egr valve it gets cooked and there isnt enough light products left to completely burn when it arrives at the cylinder. this leaves a hard carbon on the head surface and the top of the piston, compression raises and there goes the head gasket, usually failes on #1 cyl next to the timing chain galley.
just my opinion, after seeing the inside of these engines.
larry perkins lou ky 85 old cars