I have a Microsoft PS2/USB optical mouse I'm partial to, no longer available at retail, and right click stopped working.
Took it apart, the switch operated normally but the contacts were not closing. It's tiny and plastic - not repairable. I considered swapping in the scroll wheel switch, since I wouldn't miss it, but noticed the board was silk-screened and drilled for a larger rectangular 3-pin switch as well as for the square 2-pin one currently installed.
I dragged an ancient Microsoft mouse out of the junk bin and desoldered a 3-pin switch - fits and operates perfectly.
The old switch appears to be of higher quality - maybe I should have swapped them all while I was there :-)
Sunny