That comment suggested scroll ring failures on a Kensington Expert Mouse (it’s a trackball) might occur when the apertures become misaligned from the IR emitter-detector pair, although later results were equivocal. I tore apart a failed unit to see what the alignment looked like for a known-bad scroll ring.
The right side view shows the receiver roughly centered in an aperture:
The left side view shows that the ring is almost flush against the circuit board, with the isolating cutout just in front, and it’s not obvious how to lower it any further:
So I think there’s no way to realign this one, other than to raise the aperture ring a bit, but that doesn’t seem like it would make any difference: the detector already has a good view of the emitter.
If your trackball has a failed scroll ring, tweaking the aperture ring’s alignment certainly can’t hurt: try it and report back.
If you don’t expect a miracle, you probably won’t be disappointed, alas.
The pix come from the Canon pocket camera mounted on the macro lens / illuminator, handheld with manual focus. The dust speck on the detector is just slightly out of focus, but you get the general idea.