Most rear main seal leaks are caused by a combination of normal wear in the crankshaft & seal and the drying, hardening and shrinking of the main seal. Bar’s Leaks Rear Main Seal Repair restores the seal to like new condition and also contains additives to stop leaks in severely worn seals and crankshafts. Compatible with all petroleum based engines oils including high-mileage and synthetic. Works with ALL vehicle types including gasoline, diesel and turbocharged. Specifically designed to seal rear main leaks, but also works better than a conventional stop leak on all other leaks. This includes the timing cover seal, cam seals, O-Rings and other gaskets.