Does any one know if there is a difference between a mercury bought rear main seal and a GM seal for a 502 gen 6 ? I don't think the rear mains seals are stainless steel from merc but I could be wrong. I think they are both steel and made by national. Please advise.....also does anyone know the GM tool number for installation.

Ya don't need a tool .I just push it in with my fingers.

The kits I just got from fel Pro has the national seal in it .there tanish green and feel rubber coated on the outside and metal encased.

I do not think Merc uses anything special. I just pulled mine out and Merc used a GM Seal. If your engine is apart, I allways just get the rear cap on and snug it with the bolts. it will install easy at the point. Get it in the right place then torque the cap. It is important to notice that all the way up by the crank is a 1/8" groove that is deeper. The seal stops before it hits the groove so the seal has eqaul clamping force. Do not push it up until it stops. I would also scotch bright the crank where the seal runs. Make sure it looks plum & true. If the seal is all you need , the tool work best.