This is not a full tutorial, but more like a (incomplete) documentation of the procedure. Assumption is that you have the tools and some skill at their use. I'd also like to apologize for the poor quality smartphone pictures used here.
Not all of this equipment is strictly necessary, but all of it is quite basic electronics repair stuff and certainly will make things easier.
The actual parts (also shown in the picture above) I used were:
First, you need to remove the "skates" (e.g. the plastic slidey things glued to the bottom of the mouse) in order to access the 3 Philips head screws holding the mouse together. NOTE: It is quite likely that the "skates" will become unusable when removed, so you will probably want to get new replacements. Can be found from various sources, like eBay and Mouse Club. With proper material, you could make them yourself too, I suppose.
After removing the screws, the case should open easily.
The order here is a matter of preference, but the first thing I did was disconnect the connector (1) for the wire to the top case and side buttons. The connector can be very tight and annoying to pull out, so some people might prefer to take the the PCB out first by removing 3 screws holding the PCB (2).
To remove the side/top buttons PCB assembly from the top case, remove the 2 screws (3). Further disassembly is optional, though may be easier for cleaning purposes etc.
At this point you probably should clean the mouse parts. Mine had a .. substantial .. amount of gunk, hair, dust etc accumulated during the ~7 years of use. NOTE: If you end up cleaning the scrollwheel assembly, you will want some kind of new grease for it. I have no idea what would be good to use, though. Personally I just used Q-tips etc to remove the excess dirt and left the old grease in.
After main PCB is removed from the case, desoldering can begin. I did not bother with disconnecting the USB cable, as the connector was very stubborn and it was not really necessary anyway. The procedure I used was as follows:
Basically very much same as desoldering.
Nothing much to say, just do the disassembly in reverse. TIP: Do not put in the new skates before you test and ensure that the mouse is working! :)
While installing the mouse wheel assembly, make sure that the spring and the "ticker" (?) are in correct place and orientation, as shown below images.
Images of the side/top-buttons PCB assembly.