Nothing's more frustrating than not being able to use the scroll wheel on Apple's Mighty Mouse (now just the Apple Mouse). While Apple recommends a lint-free cloth and water, it doesn't work in many cases, so here are two options that don't require disassembly.
Option #1: Using Paper
1. Create the Cleaning Surface
After unplugging your mouse or removing the batteries (just in case), place the sheet of paper on a cushioned surface (such as a book).
2. Clean the Ball
Hold your mouse upside down and drag the ball with slight pressure (still letting it rotate) across the paper. You'll see the gunk come off as you do this. Once residue ceases to come off the ball, it should work better.
Additional notes: This removes some grit and grime, but in my experience the roller ball still does not function at 100%.
Option #2: Using Tape
- High quality Scotch Tape
- Utility knife or scissors
1. Cut the Tape
Cut a 3" piece of clear scotch tape to about 1/8" in width with a utility knife.
2. Feed the Tape
After unplugging your mouse and removing the batteries (just in case), begin to feed the tape (sticky side up) below the ball. This is tricky, but once the tape grabs hold of the ball all you need to do is apply slight pressure while rolling the ball away from the tape so that it takes. Using pressure and patience, eventually the tape will emerge from the other side. Use your finger nail or utility knife to unstick the tape from the ball so you can feed it all the way through.
3. Buff the Ball
Gently tug the tape back and fourth, buffing the underside of the ball. Repeat until the ball is clean all the way around.
Additional notes: This is a satisfying and effective cleaning method.
When All Else Fails ...
If the above measures fail, you may have to resort to disassembly. This method is not for the faint of heart. While I won't cover this method in this how-to, below is a video guide via Youtube: