This valve cover gasket seals the joint between the valve cover and the cylinder head on the host engine. It prevents oil leakage from the valvetrain area and keeps contaminants out of the engine oil system. A degraded gasket allows oil to weep onto the exhaust manifold or engine block, which can cause smoke, oil loss, and eventual corrosion on the sealing surfaces. The original-manufacturer gasket is molded to match the cover's groove profile and the head's sealing face, so it compresses evenly when the cover bolts are torqued to specification. On reinstallation, clean both sealing surfaces and replace the gasket; do not reuse a compressed gasket.