This type (B) does not form part of the cone, type A forms part of the cone nylon extends into and forms part of the cone.
Some Airsporter owners bought the O ring conversion for the Mk1 or 2 but soon found out what a bad idea that was.
To remove the old washer, it can be carefully cut off.
I also have made a couple of tap blanks ready to lap in. The Lever and Tap (plug) are made of Stainless Steel.
For Early Airsporter Lovers. I have made some Mk 1 and 2 taps in stainless steel with stainless steel levers. I have left the pellet hole blank so the the tap can be lapped in and then the pellet bore drilled and reamed for perfect alignment.