On my DS3, the R2 button was lose because the spring was broken so I decided to open an old sixaxis controler I had and take the spring from this one.
Opened both and replaced the broken spring closed both and they both work perfectly ( appart from the loose R2 button on the sixaxis obviously ). I didn't go as far as the D-PAD but just remember every step, remember what goes where and don't lose anything and as said above, be VERY delicate. You also have to be very patient because you will spend some time with it.
An other advice, once you put the control back together, don't screw it yet. Just hold it in your hand and push every buttons, if it doesn't feel right or if you cannot push some buttons then reopen it and see what's wrong. Don't close it completely until your controler feels as good as new.
