I used a G2 for about 2 years without a problem.
I now own a E2D and a 6P LED Defender.
I changed the lamp assembly on the E2D once after about 4 years of use.
Now, back to the G2, you could have a lemon, but if it's possible, go to a store, or gunshop (they usually sell Surefire stuff) and swap the lamp there. Sometime they come in little bags that can be opened for testing... if it fix the problem, you buy, if not, you don't.
A deffective tailcap button is something new to me. If I was closer to you, I would have told you to send it to me so I could check it out at my local store with spare parts. Maybe someone you trust in your erea can do the same.
If it's just the tailcap button, buy a compatible clone tape switch and use the G2 on your airsoft gun.
Surefire product are supposed to be LIFE TIME WARRANTY. except for the bulb and batteries.