My real question, after several hours spent removing the old faucet (progressing from tapping the basin wrench with a mallet, to an overnight soak in penetrating oil, to cutting it off with an air grinder) is "what idiot engineer uses a mild steel washer in a wet environment?" But it looks like they all do, or at least the ones who designed the new faucet do, so ...
On the assumption that I or someone else will someday want to change the faucet, what can I use to prevent the nut from freezing to either the washer or the faucet body? If I were working on a car, I'd use thread sealing compound. Does that make sense in this application? Or are there any professional tricks that aren't quite as messy?