Perhaps i am the only one who is still using this old mouse. If not: print it and use it! Otherwise: get some inspiration for your own repairs! :)
The scroll wheel of the Microsoft SideWinder X3 mouse is well known for its self dissolvable capabilities.
After a few years the rubber of the wheel gets sticky, it is expanding, and finally you have to throw away your mouse, or dismantle the rubber coating of the wheel (which was what i did).
Because i like the mouse (and repairing broken stuff), and the design of a new coating is too easy, i went the long way, designing a full plastic scroll wheel assembly with all the features of the old wheel.
Printed with a 0.3 mm nozzle and PLA.
Printed upside down (with the thin axle at the bottom), and with support, to slow down the printing process, allowing the axle to cool. Otherwise it would deform and handicap the scrolling function later.
I was not able to test if the detent works as expected, because the corresponding part in the mouse is broken too. (Next project?)
A slow printing speed is advisable.
Screenshot of the 3D model in Fusion 360.