Recently I had air leak issues with my S410 carbine. Ordered a seal replacement kit from Jim Stanis at Precision Airguns and Supplies. What I received was a packet from Air Arms labeled 'P/N S700 Export Pack'. It contained all the seals used on an S410 except the Firing Valve Body Seal and the gauge sealing ring.
The fill valve has 4 'O' ring seals. The two 'O' rings that seal the fill fitting(P/N S474)can be changed without disassembling. The Male Connection 'O' ring P/N S484 and the fill valve 'O' ring P/N S327(S328 on diagram)require disassembly for replacement.
The Male adaptor P/N S472 has a 'flat' machined onto it to accept a wrench.Ideally, the spanner wrench would serve as a 'backup wrench' but my home made spanner was not up to the job. The Male Adaptor was tightened so tightly that I had to clamp the Filling Valve body in a wood lined vise to loosen.
The existing gasket on the fill valve (P/N S327or S328)needed to be cut off as I couldn't get it off any other way. Here's a close-up of the valve without the seal.