Yesterday I finished cleaning up all of my vintage metal track via the following steps:
Hydrogen peroxide soak to undo yellowing in the plastic
CLR flash-bath to de-oxidize the metal rails
Detergent scrub to remove residual oils & solid matter
The result is this big stack of pieces of various ages that now look the same, with light, even wear. I'll give the tops of the rails a brush with ultra-fine sandpaper once they're placed in a layout to even further improve their condition and ensure maximum conductivity with 9V motor wheels!