Always replace both halves of the rear
Crankshaft Seal as a unit. While the replacement of this seal is much easier with the engine removed from the car, the job can be done with the engine in place. Remove the oil pan and oil pump as previously described, then take off the rear main bearing cap from the engine. Using a screwdriver, pry the lower half of the Crankshaft Seal from the bearing cap. To remove the upper half of the seal, use a small hammer and a brass pin punch to roll the seal around the crankshaft journal, tapping one end until the other end protrudes enough to pull it out with pliers. Clean all sealant and foreign material from the cylinder bearing cap and case without using an abrasive cleaner. Inspect components for nicks, scratches, or burrs at all sealing surfaces. Coat the seal lips of the new seal with light engine oil, avoiding oil on the seal mating ends. A small plastic installation tool should be included with the purchase of the rear Crankshaft Seal; if not, make one by cutting an old feeler gauge blade. Position the narrow end of this tool between the crankshaft and the seal seat to protect the new seal from damage. Raise the new upper half of the seal into position with the seal lips facing towards the front of the engine, pushing it onto its seat while using the installation tool as protection. Roll the seal around the crankshaft, using the tool as a protector, and when both ends of the seal are flush with the engine block, carefully remove the installation tool without withdrawing the seal. Install the lower half of the Crankshaft Seal to the bearing cap, again using the installation tool for protection. Ensure the seal is firmly seated before withdrawing the installation tools. Smear a bit of sealant on the bearing cap areas adjacent to the seal ends, then install the bearing cap with the seal and torque the attaching bolts to about 10-12 ft. lb. Tap the end of the crankshaft first rearward, then forward to line up the thrust surfaces, and retorque the bearing cap bolts to the proper specification. For Oldsmobile engines, with the oil pan, oil pump, and main bearing cap removed, insert packing tool BT-6433 or an equivalent brass punch against the seal, driving the old seal into its groove until packed tight at each end. Measure how much the seal was driven upwards, then add 16/1 in. and cut this length from the old seal taken from the bearing cap. Place a drop of sealant on each end of these seal pieces and pack them into the upper groove to fill the gap made previously. Trim the remaining material perfectly flush with the block, being careful not to harm the bearing surface. A special GM tool (BT-6466) is available for this purpose. Install a new rope seal into the main bearing cap groove, pushing firmly all around using a hammer handle or special GM tool. Ensure the seal is firmly seated, then trim the ends flush with the bearing cap mating surface. Finally, install the cap and remaining components in reverse order, tightening all parts to specifications.