After rereading #2, I see what you mean, they are talking about sealers and such... however, my first read brought me back to my chemistry background, and I recall that silicon is pretty reactive when hot. It's not going to get hot enough to melt or to coat steel, but at exhaust temps it could easily deposit on the surface of the zirconium ceramic sensing element in the O2 sensor. And that would insulate the tip and interfere with it operating properly.FYI, the Silicon contamination is not from dust/sand.
Think about what you just said and relate that to how glass is made. You'll catch on.
It's concerned with fumes, vapors and liquids.