This is our 3″ Tin Indian Performance Pontiac Viton® rear main seal. These seals are specifically designed for the traditional Pontiac block and they fit both stock and aftermarket MR-1 Pontiac blocks. The seals are made of Viton® and are far superior to the factory rope seal. They are the single most reliable way to control oil in a Pontiac engine. This product is a direct replacement for the conventional rope style seals in Pontiacs which are prone to leak over time. Our seals are made and designed by Pontiac Engine Builders and are the clear choice when you want the absolute best in oil control when rebuilding your Pontiac engine.