because the car is old and it had time to vibrate loose, the gasket hardened. its a normal thing. think of the leverage the filter housing exerts on the block pedestal as it goes through normal cyclic vibrations.

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85 300d 0m603, 717, he341, 50mm external W/G with open dump, intake manifold as well as intercooled. need to figure out a different trans before i throw more fuel at it. the 717 trans and 8" ceramic clutch are already pissed with stock elements.