May 14, 2017 · These estimates are only to replace the rear main seal. Two said $500 One said $400. One said $75 for inspection, $650-$700 labor, and $100 for parts. Can't guess on the cost, but before I spent a nickel I'd make sure it's the rear main seal that's leaking. Lots of things can drip oil off of the back of the engine, such as a valve cover, rear intake seal, oil pressure sender, front seal on your muncie or rear pan seal. Inspect the oil seal lip and the contact surfact on the flywheel shoulder. If the lip is worn or cracked, replace the seal. Note: If the flywheel shoulder contact surface is deeply grooved, you will have to replace the flywheel in order to obtain a good seal. Description: Pontiac 3.00" Main Viton Rear Main Seal (1959-79, 326 thru 400 AND 1979-1981 265/301 /Also Fits 1967 428/ Fits Early 347/370 when trimmed to fit) The updated rear main seal design requires a lot of force to press it onto the crankshaft correctly. I have tool J-45930A which is the replacement tool to J-42842. A cartridge type crankshaft rear main seal (Figure 1 - number 3) has been released for the 4.0L and 4.6L engines identified above.Rear Main Seal Install Tool . Part #: GVW-191. Works with: 1972-1991. Our Price: $49.95