It's the head gasket issue. I have a brand new Fel-Pro NOS set for an aluminum engine along with an entire aluminum engine and the car it came out of and the reason for filling that engine is to create a deck where there is none. They diecast that block and used iron liners that were captured by die cast aluminum and the gasket would weep and get to that aluminum with too many heat cycles that aluminum let go at the tops from the iron and began to chip away and fall off removing clamp surface and weeping by 50-70k miles. That's why they quit.