Tim, It is hard to say.
Only the copper gaskets seem to have the sealing ring around the area shown in Ringleaders link. I have a NOS 261 gasket and it does have the sealing rings around the steam holes but not on the holes shown in Ringleaders copper gasket.
This is a good topic.
I have seen the blue Perma-torque gaskets leak on the pass side before so I will be glad to here if it works.
