I have had my brake light switches last for years in my vehicles and a few I have sold to friends. However I had or box of nos ones that I had been using. When I did my B1d this year I finally had to install a new switch, used all the old ones I will be cautious to see if the new one fails. The other thing is I upgrade the brakes systems I do to dot 5 silicone and had read where some people felt that the silicone fluid cased the switches to fail but not in my experience.
Another option I have considered but not tried is the mechanical brake switch one example is in the link below
http://www.speedwaymotors.com/Universal-Mechanical-Brake-Light-Switch,1972.html