For those who still have the Apple Mighty Mouse and have become thoroughly disenchanted with the scroll wheel's habit of getting clogged and not scrolling (although it seems to happen only when scrolling down), I came across this simple fix. I tried it on a recalcitrant mouse and it worked! I wish I had known of this years ago, because I purchased multiple mice, and each developed the same issue. I had, in desperation, ordered a Magic Mouse 2 because it has no scroll wheel, and was supposed to get it Tuesday, April 13 from BH PhotoVideo. I cancelled the order.

BTW, I followed the suggestion in one of the comments and turned the mouse upside down on a piece of paper instead of using the paper on top. To my great pleasure, a piece of dirt popped out.