Spyder MR1 co2 leak

[Cessna 172]

I just bought a spyder MR1 from a friend and tested it a couple times at my house. I then took it actually paintballing and found that co2 was leaking very fast from a screw in front of the foregrip and underneath the barrel. I looked at the owner's manual and took apart the cup seal and it looks completely fine. No dings or scratches. Could someone please give me some advice? Thanks.

[Lawpass]

Replace the o-ring on the front plug. If its been sitting a while, you might want to clean and oil all the o-rings.