360 rear main

I need some help I have a 360 la that I’ve rebuilt and it runs great but the problem is I’m fighting a leak it leaks like the rear main so I pulled the motor and installed a new one and it still dumps oil it leaks about a gallon in 30 miles I don’t know what to do
360 rear main seal - Different PN for different years?
BS40651 felpro viton seal