This ^
But I'll add there are two potential stages to the switch overhaul. The easy "stage 1" is unscrew the retaining ring in the tailcap with a pair of needle nose pliers, take the switch out of the cap (sometimes, all it is is this ring being loose), clean all contacts (I like DeOxit for this, but alcohol is fine). Reassemble.
If it's still dead, and you are clever and coordinated with small mechanisms, you can do "stage 2". After removing the switch, you will find that with an exacto, and I have not been inside that particular switch, but usually you can just work the blade edge into a parting line and start the two halves of the plastic switch box apart - some can have little clips on the side you need to flex open. Inside there will be a spring, so be cautious and work over a table. Note the orientation of the few parts inside, and repeat the "clean all contacts" exercise, and reassemble.
I know that sounds like a pain in the keister, but all of the switches I've done that too, and treated them with DeOxit and ProGold, seem to work much better than when they were new, and I like the challenge.
Good luck!
