Here's the switch which is just inboard of the right foot peg (and nicely exposed to any water thrown by the rear tire). To remove the switch, I used a pair of needle nose pliers to remove the return spring from the brake lever pivot. You can leave the spring hanging from the switch, if you wish. Remove the right side bodywork panel and set it aside where it won't get damaged. Locate the switch's wiring connector (which is behind the turn signal relay) in its recess/support (the relay is to the rear and above the battery). Release the locking hook and separate the connector halves. Holding the knurled adjuster with an index finger & thumb, rotate the switch body, counter-clockwise, until you can pull the entire switch assembly from the circular lug (welded to the frame). You can now remove the return spring (if you haven't already), knurled adjuster and lower rubber water seal from the switch body. Set those parts aside, in a safe place.
Now the more difficult part of the process; pealing back the upper seal and removing the internals from the switch body. I have no pictures of this (sorry) and it will be hard to visualize unless you have the switch in front of you.
The upper seal can be pulled back from the top of the switch. However, the protective wiring sleeve is molded to the wires so that the protective sleeve will not slide. So, pulling back on the sealing cap will put undue stress on the wires at the top of the switch. I used a small screw driver to gently fold the cap back, thus turning it inside out, over the protective sleeve. Now you should have full access to the top of the switch body.
At the top of the switch (again no pictures - sorry) there is a white plastic plug held in the switch body (black plastic) by two protruding tabs. These tabs lock the plug in place by snapping into corresponding square holes in the switch body. You almost need three hands to release one of the tabs with a very small, flat-bladed screwdriver while squeezing the top of the switch body into an oval shape which (hopefully) will allow the other tab to release. It took me a few tries before coming loose. Resist the urge to pull on the wires, you may separate them from the flat, metal electrodes within the switch (thus compounding your issues).
Once you get the switch body to release the tabs on the plug, you'll see this:
Sorry for the poor picture quality, my cell phone camera was having trouble focusing on the small parts.
Here's a (somewhat) better image of the very dirty switch electrodes:
And the switch plunger:
It's pretty obvious that the issue is filthy electrical connection points but a closer inspection reveals actual wear:
Here's the switch plunger after being cleaned with a piece of Scotch-Brite. Notice the two grooves worn into the metal band on the plunger. The opposite side was worse (although hard to see):
On this side, there is an actual low spot where wear and corrosion have left a void. It obvious that the switch has been in one, un-adjusted position for its entire life. Given the fact that I will most likely have to properly adjust the switch, upon re-installation, the electrodes should not ride in those wear groves (hopefully).
I cleaned the (delicate) electrodes with some distilled white vinegar (which almost every household should have - if not, it's very cheap at the grocery store). You may also use fresh-squeezed lemon juice. Here they are after a chemical cleaning:
The tarnish is gone but there is still some actual dirt. So, I used a piece of 1000 grit wet/dry sandpaper to remove the rest of the dirt. The ends of the electrodes are bent into a "v" shape so they will encircle the metal cylinder on the plunger. Using the folded edge of the sandpaper, I was able to get into the "v" and remove the remaining corrosion.
Ready for re-assembly.
The pink arrow indicates the knurled adjuster and the yellow arrow indicates the return spring. Installation is the reverse of removal; place the adjuster into the frame lug (you may need to remove the lower seal to get the switch body through the adjuster), screw the switch into the adjuster (clockwise), replace the lower seal (if necessary), hook the spring onto the switch plunger and then use needle-nose pliers to replace the spring onto the brake lever pivot arm. Don't forget to check the adjustment! To do so, plug the switch wiring connector back into the main harness (and secure the connector into the recess/support). Turn on the ignition (the headlight and tail light should illuminate). Press down on the brake pedal and observe the brake light. If the light comes on with the pedal depressed and goes off when the pedal is released, you're done.
If the brake light does not come on at all, the switch is too low (too close to the brake lever pivot). Hold the switch body steady and turn the adjuster clockwise (which will raise the switch body). Continue to test and adjust until the switch works properly.
If the brake light is on and stays on, the switch is too high (too far from the brake lever pivot). Hold the switch body steady and rotate the adjuster counter-clockwise (which will lower the switch body). Continue to test and adjust until the switch works properly.
Feel free to leave questions or comments in the Comments section. I'll do my best to respond to everyone.
Also, remember the fear about expensive switches and their availability? Total over-reaction. The switch is still available, from Honda (part #: 35350-MK3-405), for about $10 (US) as of this writing. I'll be ordering a new one so that when/if this one dies, a new one will replace it.