I would hold off dis-assembly and begin instead by sitting the machine in a shallow pan and repeatedly sloshing kerosene through it. Dab with a stiff, stub (cut-off) brush where you can reach. Best done outdoors because of the stinky quality of kerosene, but it works beautifully as a solvent and temporary lubricant. After it dries, you'll have to lubricate with standard sewing-machine oil. The 31-15 is a simple machine, so it should respond well to this treatment, and flush superficial oxidation.
Maroon sounds nice. Please post photos when you do it.