This Preliminary Information communication provides additional information to the technician when replacing the Duramax Diesel head gasket. This is a supplement to procedure found in Service Information. The left and right cylinder head gaskets are not interchangeable and will block oil and coolant passages if installed incorrectly resulting in severe damage to the engine. Technician is not use any power sanding devices, wire brush or wheel as well as any chemical cleaning agents to clean the gasket surface. Leave the gaskets in the package until the surfaces are ready to install them. Do not set the gaskets on workbenches or tool boxes to avoid introduction of foreign debris. The cylinder head surface is not to be machined measure the head for warpage with a straight edge and feeler gauge replacing the head with warpage in excess of .1 millimeter. All M12 head bolts must be replaced however the M8 bolts can be reused. Install 2 head bolts secured at minimal torque to minimize the chance of introducing foreign material. Use a paint pen on the M12 bolts marking the head of each bolt indicating which of the 4 torque steps have been completed to prevent missing a step or doing a step twice.