PS3 Controller L1 button not responding

I dropped my ps3 controller accidently but it wasn't a heavy impact nor did I step on it. However L1 button stopped working completly. Everything else works fine. So i tore it apart to find out about this problem and I found out that there was nothing broke. But the black strip pad underneath the button rubber is not responding. I tested L2 works just fine when i push down the rubber but no respond on L1.

Now I did some google search but I didn't find anything about this, anyone else has this issue that can help me?

I attached picture to show exactly where it is.

http://imageshack.us/photo/my-images/135/brokecont.jpg/

Buy a new controller. The PS3 controller is just a nightmare to try to take apart and put back together.