Bar's Leaks Rear Main Seal Repair is the first off-the-shelf solution to stop rear main seal leaks, as well as other major oil leaks. Bar's Main Seal Repair works with all gasoline and diesel engines using conventional, high-mileage or synthetic motor oil. A single bottle is added to the engine crankcase with every oil change. In addition to repairing rear main seal leaks, Bar's Main Seal Repair also prohibits leaks at the timing cover seal, O-rings and other gaskets.