Don't all cars now have aluminum heads and they
don't fail at the high rate that MB's do. Does the
length of a I-6 head have something to do with
the failure vs shorter heads on V6, I-4, boxer etc?

Dave

91 190e 2.6 90K, on 2nd head gasket.
73 bmw 2002, Head cracked after 25yrs
96 Subaru 120K, still on 1st head gasket