3 Gaskets are designed to fill in the gap between two parts to keep oil, coolant, or other fluids inside and contaminants outside. In many cases, all you need is a gasket to prevent leaks. Whenever you add sealer in addition to a gasket, you’re being redundant and may be courting trouble because sealer is unnecessary in some applications. Use sealers only where gasket ends meet or gaps exist. If you’re going to use sealer with a gasket, limit its use.