So everytime I towed my popup I would get a small leak from the pinion seal in the rear 3rd member. Since I put Nitro 4.88 gears in my 97 4runner, the pinion is upgraded from the stock 27 spline to a 29 spline pinion. You also need to purchase a new flange kit to accept this 29 spline which also comes with a new seal and nut for the pinion. When it came to replace the rear pinion seal I forgot about the change and purchased the seal, part number 90311-38047, which is for the 27 spline pinion and will not fit the 29 spline. I had a tough time figuring out what I needed and I really wanted OEM parts. Ended up finding part number 90311-41009 which is the rear pinion seal for a 29 spline pinion, and the nut was part number 90177-22003. I believe I looked up a 2004 Tacoma to get these part numbers.

I think it was in 2003 that toyota changed the 27 spline pinion to a 29 spline in some of the rear 8" axles. So far I've driven about 1200 miles with about 250 miles of towing and not a drop of oil leaking. I'm making this post so that if in the future if I need to do this again I'll have the part numbers, and perhaps someone else with the same setup might find this info helpful. The kit that Nitro sells for the flange kit that includes the seal and nut, I cant say for sure that they use OEM seals. They looked very similar, but Nitro's seal didnt have the part number that the OEM has on it. About the only difference I could tell from the two.

I'll update this post later down the road when I've put more milage on it.