A few years ago when I put the disk brakes on the Chevelle, I installed the bare cast iron master cylinder against my better judgement (hey I was running out of time to get it on the road / out of storage). Surprising nobody, it rusted pretty quickly.
Today after work I hit it with a wire brush and masked the not-cast-iron bits. A quick coat of paint (Seymour Cast-Blast) puts it back to looks-like-new and hopefully-won’t-rust-within-a-couple-days.
While this dried I finished getting the firewall ready for paint (mainly just dusting it off and re-masking a couple things) so that should happen tomorrow. Exciting!