I have had two might mouse roller balls stop working on me so far. I was convinced by some website to try and disassemble it and clean, but THAT turned out to be a BIG mistake. The ring around the bottom of the mouse is not meant to be removed and broke apart in several pieces.
Then, upon putting the mouse back together nothing on it worked - except for - get this, the little roller ball. And even that would work only for the rolling function - it ceased to work as a button.
That mouse is now toast. Not mighty at all.
Mighty Mouse Dissection