On second thought try this first before you disassemble your rifle...remove the air bottle, set your Power Wheel to MIN, screw your air bottle back on and cock & fire a couple shots and see if this stops the air leak from the tip of the valve rod. If not remove the air bottle again, and with the Power Wheel set to MIN, turn the valve pin adjustment nut in clockwise until it bottoms out, screw your air bottle back on, cock & fire a couple times and see it this solves your air leak from the tip of the valve pin there in the magazine well.
Chuck