Having a little trouble with any G-natural! (Key Of C Flute)

[QueenMangle]

Today, we were playing through our concert music in my band class, when I noticed any of my G-naturals (middle, low, high) wouldn't come out as strong as they used too. That's the only note that seems to be off. It sounded VERY airy and weak. Yet, my G#, or any other note seems to come out as usual. I asked the other section leader (our Flute section is divided up between First and Second Flutes, I am the Second Flute's section leader *I chose to play Second Flute, I can just as easily play First, but would much rather play Second.*) if she could look at it, and maybe try to get the sound out, thinking maybe I just had an embouchure issue, or such. She attempted it, and also could get any note but G-natural out. We both took it up to our Director, who said he personally thought it could be a leak, but couldn't find the leak. Right now I'm stuck with my Piccolo until we figure it out, I just wanted to ask if anyone had an idea as to what it could be, and how much it would be to repair it. It's pads aren't in the best condition, but they are looking normal for 4+ years of playing. (the pads are going to be replaced soon, but not until a month before our marching season begins, that way it has time to be repaired when it isn't absolutely necessary to be played.)