Just a quick post on this, since it’s a problem I’ve run into with a number of apple mice. The scroll wheel has a tendency to stop working properly, usually because it will eventually get dirty and not track properly. When I looked up fixes for this in the past, it always involved opening up the mouse and messing with internal parts and screws and things I just didn’t want to mess with. However, a comment on this post related a solution that worked fantastically well. In order to clean the scroll ball, just hold the mouse upside down, and scroll the ball firmly on a mouse pad for about 10 seconds, scrolling in every direction. I tried this, and my scroll ball is now working beautifully!
Closeup of the Scroll Ball
Scrolling the mouse, upside down.