|The newer optical mice are far superior to the older mechanical variety. They give far less trouble and require nothing more than an occasional external cleaning.|
Unfortunately there are no simple instructions for reassembly of a mechanical mouse. The details very quite a bit from one manufacturer and model to another. If you don't remember how to reassemble it there is little anyone on a forum can do to help. Most people learn early in life that taking things apart is much easier than putting them back together.
My advice is that it probably isn't worth the trouble.