I just did this R&R on my machine which is coming up to 100K now. The light had been coming on occasionally over the past 10K+ miles, but decided this weekend that it wanted to illuminate my life permanently.
Anyway, I disassembled the nad switch to see what was what, and there were two small squares - like flakes- of copper broken off of one of the contacts. It's very thin, and looks like it's doomed to a fatigue failure at some point. Anyway, no chance of a simple clean-up and re-install.
I took 2 pictures, but the background is mottled so you can't even see the flakes.

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Prost!