The Rear Main Seal in the LS style engines is a Teflon Rear Main seal. These can last a million miles with no leak. The LS rear main leaks are usually the rear main plate gasket not the rear main seal.
Since these are Teflon it is necessary to install the seal DRY and CLEAN on a Clean and Dry crankshaft. This allows the teflon to impregnate into he crankshaft and you end up with a perfect seal for the life of the engine. These seals are fantastic but easy to damage on install. Fel Pro or National seals will come with a plastic seal installation tool. You slip the plastic tool over the crankshaft and press in the seal with the plastic protecting it from damage. Once installed you grab the plastic tool and pull it out. I use vise grips to grab it and pull it out. IF the bolts on the cover plate are a little loose the plate should self center to the crankshaft from the pressure of the seal on the crank. Gently torque the cover plate bolts to spec and you should be good to go. National Made these seals and supplies all of Fel Pro seals. National had the GM contract years ago but I have no idea who supplies the GM seal today. Teflon seals were first introduced on Diesel engines in the 1990's and later they were introduced on automotive engines. They are the very best when installed properly.
The biggest change on install is Clean and Dry on the sealing surface. All other types of seals need lubrication not the teflon, lubing teflon can cause leaks. The outside of the seal where it installs into the cover plate has a rubber or type of rubber seal to seal the outside/non rotating part of the seal to the cover plate. To ease this installation a thin film of lubricant/oil can be used to help reduce install effort but Zero oil on the teflon surface where the crank rotates.
If you think I am wrong on this look up Cummins, Detroit Diesel, Caterpillar, or John Deere Teflon Seal installation instructions. They have been using the technology much longer than GM.
Sad part for me, I just did the Oil pan and front main seal a week ago and now find my rear main seal is leaking also. DANG. More work to do. I hate leaks.
