The portion of piston that holds the warrors piston washer on is from memory around 3mm thick, you wont get a new seal on it without removing the steel washer on it. The front of the piston was hard steel.
I did think the best way would be to cut of the broken bit that held the washer on then bore the piston right through. Then thread it for a new piston end threaded with a flange to hold the leather seal. This would have a hole bore through its centre for the barrel.
I foolishly flogged my warrior to a member of my club a few years back. Might ask him if he will flog it me back!