I have Mionix gaming mouse that I bought in 2008 or 2009 and have been very happy with since. As any electronic device that has been in intimate contact with humans would, it has acquired a fair amount of filth over the years. Some of the grime has also worked its way into the scroll wheel which has started to act up. Recently I decided to do something about it and took it apart to try to clean it properly.
I will say right now that I didn't entirely succeed in this quest. While the mouse did get a lot cleaner, the scroll wheel still doesn't work properly and there are some corners in the plastic that I didn't manage to clean properly. The mouse is currently relegated to a junk box in the storage closet until I make another attempt at fixing it up or, more likely, throw it away. So this article mostly serves as a teardown guide.
This section is best explained in pictures.
After the top printed circuit board has been removed the side buttons can be removed from the case. I had to bend these quite a bit to get them out, but I found that they are very flexible and can take some force without breaking.
The top cover consists of two parts. A single screw holds them together.
As a first attempt I tried to simply scrub the case parts clean with a dishwashing brush and detergent. The dust washed off easily enough but this did nothing for the grime that made the plastic sticky. I let it soak overnight but this didn't do much for it either.
What finally worked somewhat was to scrub the parts really hard with an abrasive cleaning sponge. I used the lightly abrasive white surface, not the heavier green kind as I was afraid to scratch the plastic, although that might have worked better in hindsight.
I also cleaned the buttons and the scrollwheel, but this didn't turn out to have any effect on the function of the scrollwheel.
I wasn't able to remove all the old adhesive, which is what has attracted dust in this picture. Further, while the top side ended up fairly clean the ends of the case parts were still sticky afterwards.
While it looks a lot better now, I'm still hesitant to use it. The scroll wheel is still jerky and parts of the case are still sticky. Even if it had turned out basically good as new, I'm not sure I would redo the process. It was several hours of pretty gross work.
I suspect that at least some of the grime was actually the surface of the plastic that had decomposed after years in the sun, since my desk was previously next to a western facing window. Although I hate to throw tech away that mostly still works I did get a good seven or eight years of heavy use out of this ~600 SEK (~60 EUR, ~80 USD) mouse. I recently moved and in my new flat my desk no longer has view of a window so perhaps my new mouse will last even longer.