Following Dan E.’s advice, I added a few drops of 3-in-1-style lubricant. The toxic bath didn’t make the parts look new, but it worked loose most of the crud and some of the rust. (If I were less lazy, I might also have soaked the knobs and selector switch in a cup of warm water with some dishwashing detergent added.)
I'm removing a self-stick tortoise pickguard (cheap) from my 2013 Martin 000-28vs acoustic guitar and replacing it with a clear pickguard (scratch plate) usi