My spyder pilot acs paintball marker is leaking CO2 please help!!!?

it seems like is leaking from in the gun right around the valve area its almost like it can't build up pressur. i already took it apart and checked all the o-rings and they looked okay and tightened everything what i think might have started this is after i cleaned my gun i forgot the bumber that goes on the spring and dry fired once well anyways please give all ideas or answers