Converting my '72 1.8 with side shift to 5- lug and replacing output flange seals. Pulled old seals out and drivers side looked fine and new seal went in nice and flush. Passengers side seems to have some sort of " shoulder" on the inside of the surface where the outside surface of the seal seats. Looks like a wide metal ring, that shouldn't be there. I pressed in a new seal and this shoulder deformed the new seal so it wasn't nice and flush and perpendicular to the seating surface. What is it, and should I try to remove it? Pictures below.

That is cast in. You need to push the seal in so it sits flush with the shoulder.

Flush with the outer edge or the tranny case lip, or flush with the outer edge of the cast-in piece?

Flush with the casting.

I had a domestic made output seal and it was not as thick as OEM, and it actually sat below the level of the tranny case and below the machined surface exposing a bit of the race. You want it as flush as possible, toward the centerline of the vehicle. I had put a new german seal on and it seemed to seep tranny fluid, so I should have just pressed it in deeper. After installing the second domestic new one, I saw that the domestic seal was thinner than the german one. But no seepage.

When I received my two new seals, they looked different. One was in a nice blue and white box, and that one looked good. The other was unpackaged, and looked a little flimsier than the other. The boxed one is the one that went in OK.

the domestic sea, is sized 7.05 mm x 67.7 mm and is black in color. the manufacturer is Carquest. it was closeout from Rockauto.

1 - The part the seal goes against is not a race. The race is what the bearing runs on.

2- Just because a seal is not as thick does not mean that you need to seat it in further. Seat it at the shoulder, this is sufficient. The only reason to change the depth is to avoid a wear pattern on the output flange shaft. Seating a seal too deep means you run the risk of contacting the diff bearing and ruining the seal. There is no benefit in seating it deeper.

There is no size difference from side to side on the transmission output shaft bores. There may be seal variances in thickness, but the ID and OD should be identical. Seating it correctly protects from having it warp. If you are seeing significant warping, the seal may not do its job correctly.

thanks for clarification. I guess I need to pull that recent seal and install another.

Clean up the sealing surface on the output fanges with scotchbrite or steel wool. The seal may ride on a new area of the flange that may be rusty or cruddy.