PVC window Repair?

Hello,

Can anyone give me an advise of how to repair PVC window frames. My windows are about 12 years old. Leak occurs quite often and window frames seem to be distorted. They look bent because you can see the gap between the wall and the frame. The top of the frame is drawing a curve as if the window cannot take the pressure from the walls right above and both sides.
I know PVC windows suppose to last for 20 years and my windows still look new. So is there a way to fix this problem without replacing them?

Thanks,

Tammy
August 2010