This is the perfect time to replace the rear main while the transmission is off the vehicle. Remove the oil pan and slide it towards the back. The rear main seal is a 2 piece seal and is held by the rear main crankshaft bearing cap. You must remove this bearing cap to replace the upper and lower section of this seal. The upper seal requires that you use a small drift punch or equivalent, prefferably something that wont scratch the crankshaft or any surface it may come in contact with and gently tap it from one end until it rolls out of the other side then grasp it with a pair of pliers. Note the orientation of the seal of where the lip of the seal is facing and install the new seal in the same direction. Dab a small amount of engine oil on the new seal prior to slipping it into the gallley.
