You could follow the Wizard mouse schematic on Ian Stedmans' website and see if you could modify a PC mouse into a Amiga mouse (Never actually done this myself, but I don’t see why it wouldn't be possible).
http://www.ianstedman.co.uk/Amiga/amiga_hacks/Amiga_mouse_repair/amiga_mouse_repair.htmlHodgkinson.
EDIT: If either of the Tx or Rx sensor pairs on one of the opto disks has become miss-aligned, that can stop that axis from working. Muck also has the same (Although cumulative...) effect.
