actually the "wheel" on the side is just to buttons used for "document quick-flip" its like pressing alt-tab but they built it into the the side with a half wheel that doesn't spin. you can change it so it zoom's in and out for web pages if you want.
the main wheel is really cool though since it can go from free spin to clicking by pressing it down. the free spin lets the wheigt of its wheel spin really fast to go through documents faster.
i have one and paid 100 (just after its to late to return, of course) its dropped to 79.99 but ohwell i like it a lot.
as for the issue at hand i would recommend the MX revolution as a replacement and the one you found to attempt to change the guts.