Time to quit protecting my ego and ask some questions. r/Airsoft, I can not figure out whats wrong with my GBB magazine.

I have a KJW Sig p229 and it is ffreeaking amazing. However there is one issue I am having that I can't figure out how to solve. Whenever I fill the magazine with gas, the O-ring always comes out. Sometimes it full on flies out, sometimes it just gets lifted. I do use propane instead of green gas, so is that a part of the problem? And while I'm on the topic of green gas and propane, is there any difference between the two? I put silicone oil in a little reservoir so my gun still gets lubed, but my friends still give me shit for using propane instead of green gas saying its bad for my gun and whatnot. Whatever. Also what is the screw thing on top of the fill valve? It looks like I can use a screwdriver and twist it but I don't know what that does. My biggest issue though is the O-ring thing so if anyone knows how I can fix it that would be awesome. Thanks.