My 1st gen Razer Diamondback's scroll wheel finally gave up today. I took it apart to see if it could be repaired, and found years worth of dust and cat hair.
Unfortunately, it appears that the shaft on the mouse wheel that turns the wheel of the encoder has worn out. So it no longer can make contact with the inside of the encoder wheel. I attempted a quick fix using a thin layer of hot glue on the shaft, but that doesn't seem to have helped.
Oh well... for a 15 year old gaming mouse, I think I got my money's worth out of it.