Where does this O-ring go?

[sd_iconoclast]

I just bought a new rear main seal for the 3100 that I am rebuilding.
It came with an O-ring that is about half an inch in diameter.
I cannot figure out where the O-ring goes.
Does anyone know?

[Ed_Mc.]

If I recall correctly, the O-ring seals an oil passage between the block and the removable half of the rear main bearing assy. There's a machined recess there for the O-ring to fit into.

HTH........ed

[sd_iconoclast]

If I recall correctly, the O-ring seals an oil passage between the block and the removable half of the rear main bearing assy. There's a machined recess there for the O-ring to fit into.
HTH........ed

This kind of matches what I thought. The problem is that I do not seem to have the machined recess in this area. Is it only on certain blocks?
Is ithe recess in the block or in the bearing cap?