Should be same as Witness, very easy. Take out large grub screw at bottom of mag. With a long flat blade screwdriver take out the piercer unit which holds the seal, (THIS HAS A LEFT HAND THREAD). A small washer shaped piece of white Teflon is used around 8.1mm x 3.15 x 1.6mm thick. Teflon is poor quality for this application but does the job for a while. If you can cut out a piece of polyurethane with a leather punch it will do a better job. I make these polyurethane ones myself on a lathe with core cutters and a scalpel.
Baz