Before you replace the rear transfer case output shaft seal, raise the vehicle. If there are shields on the transfer case, take them off. After that, take out the rear propeller shaft. After that, disconnect the rear output shaft seal in the transmission. For the installation process, use the j29162 (Rear Output Shaft Seal Installer) and prior to installing, put a small amount of automatic transfer case oil gm p/n 12378396 on the seal's mating surface. After that, install the rear propeller shaft again. Examine the level of oil in the transfer case and place more as necessary. After that, fit the transfer case shields and then set the vehicle down on the ground.