One day my R2 trigger refused to work all in a sudden. The second day it spread to my square button. I dissembled the controller to this step and found some liquid between the green motherboard and the black plastic holding it. I should not have bought a second-hand especially for a launch version. Anyways I cleaned it up and it still didn't work. I then went to ebay and bought a new motherboard. Basically it is a piece of delicate plastic like PCB. It is held in place by 3 plastic columns and 3 gaps for sliding underneath both triggers and the touch pad. Sorry for no pictures but a careful removal of the old one would give you the best illustration of how to put the new one back. First remove the rubber pads of the triggers, which allows you to slide in the PCB. Then there are another 2 small plastic columns at the back of the gap near the touch pad. There is no need to detach the rotors. A pair of tweezers would help greatly. My controller now works perfectly like new and thanks to the author.
if you lost the springs unfortunately, the triggers would still work but it is harder to get to the precise digital press. In other words you will have hard time to create a light press than a hard press.