Need help with a leak in my Infinity

[Pelletnutz]

Have a leak at the muzzle end of the air reservoir. I took the end cap off an it looks as if one of the orings is splitting all the way around the outside. Does not look normal. I can not find any diagrams for this particular rifle. The one I found has a different end cap and fill port. Any info would be helpful about oring size and where I might be able to buy some replacements