The rubber membrane cover on my Garmin 810 power switch failed, but was still somewhat attached, so I've been using it normally for several weeks, once, even in a nasty rain ride. Today, the cover came off entirely, leaving the switch exposed, but hard to reach down inside the case. I Googled "810 switch repair" and found a video that, while useful, was more trouble than I wanted to deal with. I figured out a repair that is basically free, and takes longer to explain than to actually do. I took a largish rubber band, like from a bunch of asparagus. It needs to be about 1/4" wide, and cut to approximately 1.4 to 1.5" long. Roll up the rubber band to fill the oval hole in the case, trim it flush to the cover and apply electrical tape to seal it to the case. Easy, and it works.
Missing waterproof switch membrane and exposed micro switch. Large rubber band used as photo prop.
Cut rubber band to about 1.5" long.
Roll cut rubber band and fit into oval hole in case. Test on/off function by pushing on side of rolled band.
Trim exposed part of rubber band flush to side of case. If your blade is as rusty as mine, be very careful!
Finish off with good quality electrical tape.
Check on/off function, go for a ride!