When I was working on some oxidized track, that still had good conductivity in the joiners, a rag with some CLR or other other acid-based cleaner worked great.
I found much stronger stuff at Home Despot under the Zip brand.
Just enough to remove oxidation. When I had loose sectional track, I dipped the joiners in a cup of the stuff.
I rinsed off with a hose thoroughly. The allowed the weathering on the side of the rails to stay, and the tops nice and shiny.
Clearly this will not work well for organic buildup, heavy corrosion, etc.
p.s. degreasing and overall cleaning in a dishwasher works well, time when wife out shopping... ask me how I know.