I had the same button on mine go out. I had to go through Thrustmaster who had me go through a bunch of hoops like take a video of the problem and then before sending me a replacement, cut the USB cable on the old one and send them a pic of it.
LOL although I just spliced it back together and gave it to someone else who needed a HOTAS. But instead of waiting I just went ahead and got a X55 and haven't looked back. Gave the replacement T.Flight to my 11 year old son for ED and its perfect for him.