I know I am resurrecting a zombie, but here are some images of the controller.
The "front shield" is very hard to get off. YOu'd need something to press the plastik nose towards the inside of the controller at the right spot.
Getting the two halfs apart is easy when you move one side just a bit to the back - the other side has small hooks at the end (see pictures).
Unfortunately, mine is beyond repair as the small white ring with the pressure points lost one tooth - one of the eight directions will be lost.
Maybe I can insert some metal lever instead...