If doing O-ring replacements only, you want to be sure to use viton or equal for high pressure applications/heat resistance.I used to rebuild and customize paintball guns. I'd take it apart and see if I can find matching O-rings and replace them all, then re-oil it and see if it works. There are standard sizes for O-rings, you just need to get the right diameter and cross section sizes. The black O-rings are either neoprene or Viton. The lighter colored ones are probably nylon.