There are ways to get more life from the original Amiga mice, depending on how it was originally manufactured (seems Commodore farmed production out to several companies).
Movement: the rollers and ball can be cleaned with mild dish soap to remove the finger oil that causes them to slip over time. Naturally, you should not get the electronics wet.
Mouse buttons: Most of my mice from Coomodore employ a cheap switch (a small square package with 4 legs and a round button on the top) under the mouse button on the circuit board. Over time, these wear out, but, there are 2 contacts inside. That's why there are 4 legs. On some designs, you can de-solder the switch, rotate it 180 degrees, and reinsert it. Sometimes this works well until you can get a better quality mouse with real microswitches. I have tried to put better swithes in the original mouse, but, the dimensions are different and the mod tricky.
Good Luck
