How to fix wii u gamepad zl and z buttons?

I had my wii yo for about 2 years so it is no longer under warranty. I hardly ever use it, I have never dropped it or spilled anything on it. I recently baught the new Mario kart game and realized the zl z buttons are not responding. I do not know if these buttons were broken when I bought it of they suddenly stopped working since I do not remember using these buttons for any other games. Is there any thing that I could try to fix it. It seems a waste to buy a new one since buying an iPad is only about 50 buck cheaper than buying the whole system again and I just spent a ton of money on a new game that I can't use properly. This is the second time I had an issue with wifi u since I already had to send the actual system for a repair before. Love Nintendo games but hate the quality of their systems and accessories.