Raise the vehicle and support it securely on jackstands. Remove the driveshaft, noting that some transmission lubricant may drain out when the driveshaft slip joint is withdrawn from the extension housing. To remove the oil seal from the end of the extension housing, use a special tool available at most auto parts stores, or if that is not available and access allows, use a thin blade screwdriver or chisel to pry the oil seal out. Inspect the sealing surface on the driveshaft slip joint for any scoring or burrs that could damage the new oil seal; if the yoke is damaged, it should be replaced. Check the extension housing counterbore for burrs and remove them with emery cloth or medium grit wet-and-dry sandpaper, then clean any sanding residue with a cloth dipped in solvent. Apply silicone sealant to the inside diameter of the oil seal and grease to the end of the rubber boot portion. Using a seal driver, large socket, or section of pipe, install a new oil seal, ensuring it is completely seated in the counterbore. Reinstall the driveshaft, lower the vehicle, and check the transmission lubricant level, topping up if necessary.