It`s only an "o" ring on the pin itself, they go from time to time, It`s not a problem to repair but the bottle must be out of air to do it, the top simply unscrews, If you can`t do it maybe get yourself to Ambush Paintball at Botley which is near you , I`m sure anyone would fix that for you, the reason it`s ok when you screw it onto the Gun is because it flows direct into the gun which in it`s self is what it`s supposed to do.