I think I bought it from the pellet shop. The hole is aligned with the rail and no dirt or debris. Have been looking for vids on youtube and have seen a few with same issue but just complaints no repairs or explanations.Is the fill port hole on the bottom of the gun perfectly aligned with the metallic looking rail that has a slot in it? If you take the tank / reg apart you have to be careful not to screw them back in too much. You might be able to insert the fill probe but it might be pushing against that metallic rail and messing up your o-ring seal.
Although as you mentioned the air blowing out through the fill port, I think this is a different issue than I described. Not sure about that. Who'd you buy the gun from?
One screw holds the other screw in place and also there's a tiny O ring On the bottom Screw If you If you change that o ring out don't overtight it the other screw holds it form moving around Just tighten it snug It can leak air there as wellIn the tube next to the regulator there is a screw next to another screw that looks like a jam screw. What are those for and what are they supposed to be set at.