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He isn't talking about the gasket between the manifold and the head.

One thing I've noticed is that most muffler shops will make you an exhaust and will use a 3/8 bolt, which is a no-no because the hole in the manifold is something bigger (I think 7/16 but it's been awhile, I no longer run stock manifolds). The small bolt in a big hole allows everything to move around too much which causes gasket failure. But now that I typed all that, it will probably end up being something else.



Originally there was no gasket on the pipe, or head, side of the manifold. The gaskets are to take up slack ( So to speak) The mating surfaces have to be flat and even with each other. As the system heats up the seal should get tighter. If not the system will continue to leak as soon as the gasket gets burned out. I never had an luck stacking gaskets, ( 2 or more) but you just never know.