OK, I believe it's the CP2410-1RK that you need- the other kit was a red herring, as the Pagehiln m/cyl is 0.7" (about 17.8mm) bore - well mine is anyway. I don't know why yours has an O ring as both Pagehilns that I've seen have a pair of lip type seals, one cup-shaped and one ring-shaped. The cup shaped one goes between the spring and the piston, while the ring one goes in the piston groove.