My spyder pilot is leaking, how can I make this stop?

hi I have an 05 spyder pilot acs blue/black fade, and where the co2 tank goes in, (can't remember what the things actually called), there's a small hole there, and it leaks out. I know that it's supposed to come out sometimes but it's slowly leaking constantly and I don't like to waste air. Also I like to keep my co2 screwed in due to the co2 lost from unscrewing the tank. One last thing is there's a screw that holds the co2 inserter thing on, and its missing a screw. It usually has 2 screws holding it on. Is this why it's leaking? Thanks!!!