If your buttons are sticking occasionally, you can refurbish them using
Novus Plastic Clean & Shine. Push down on the white tabs and pull the button out of the black casing to remove the button top from the shaft. Then, you can clean dirt out of the button that can cause sticking. If the button still sticks, you can use Novus Plastic Clean & Shine with a felt polishing bit attached to a Dremel to smooth out the plastic parts of the button that contact the casing as well as the casing itself.