Well, that problem is solved. I will reserve the Polident tablets for the thermos jugs and crystal vases! I appreciate all the info.
I am going to try Evapo-Rust on the one with the rust spots, and alcohol and/or sewing machine oil on the rest. The alcolhol won't be anywhere near the machines. The feet aren't really dirty; most of them have sat in antique stores for years and years and are just dusty/grimy.