Thanks for the input guys. Firstly a BB is a ball bearing. I now know the 2 cylinder seals are the same; cylinder to body and filler block to cylinder.
If anyone needs to know these are BS 116 70A Nitrile. The one inside the filler block in which the BB seals is BS106 70A Nitrile. Gun is back together first couple of shots through chrono recorded; then onward daily for the next week to confirm seals are a success.