2001- Later GMT800, 2500HD, 3500 with 6.6 liter Duramax diesel engine The rear seal is press fitted to both the engine block and crankshaft. Fit of inner/outer seal bodies is critical and any misalignment can result in leakage. GM-44642 is a two-piece tool that mounts to the crankshaft and forces on both inner and outer seal bodies. Place the new seal on the inner body of GM-44642. Attach the tool to the end of the crankshaft assembly. Turn the forcing screw on the tool to press the seal until it bottoms in the block.