Sorry, I could only get you these. The board bottom has basic phillips drive screws but the sensors themselves have large Torx screws I don't have a driver for. But here is the opened underside.
Personally I've noticed some of the software (games) for the Wii will sometimes lose sensitivity after a period of time playing, similar to an un-homed stepper motor over time losing steps. But if this isn't that sort of problem check the the cable connector between the battery compartment and the main board; the cable connector can be pulled out/put in pretty easily. The compartment only has two screws but can only be pulled up after the main underside comes up. Feet come off first. Hope this helps :)
P.S. There are no hidden screws or out-of-the-ordinary bit drivers needed to open it up