The Rear Cover Gasket is a component that sits between the rear cover and the differential housing, forming a seal to prevent oil from leaking out. It is typically made of rubber or cork and requires replacement if it becomes worn or damaged. The gasket creates a tight seal that prevents contaminants from entering the differential housing, which could cause damage to gears and bearings. A properly functioning Rear Cover Gasket ensures that there is sufficient lubrication in the differential to reduce friction and wear on its components, resulting in a longer lifespan for the vehicle.