A valve cover gasket is a component that seals the gap between the valve cover and the engine cylinder head. It is typically made of rubber, cork or silicone and prevents oil from leaking out of the engine. The gasket also helps to keep debris and dirt from entering into the engine, which can cause damage to internal components. Over time, valve cover gaskets can become worn or damaged due to exposure to high temperatures and constant pressure. When this happens, oil may start leaking out of the engine causing potential damage or fire hazard.