Is it an ally rocker cover? How about this DIY recipe?
This recipe will make your own aluminum cleaner that will remove tarnish and greasy film from cookware and surfaces.
To make 8oz/225g cleaner
8 tablespoons cream of tartar
8 tablespoons (baking soda) bicarbonate of soda
4fl oz/ 115ml white vinegar
4 tablespoons soap flakes
Combine the cream of tartar and baking soda in a medium-size bowl. Add the vinegar and mix until the ingredients form a soft paste. Add the soap flakes. Transfer to a jar or bottle with a secure lid and label it clearly.
To use, apply with a steel wool pad, then rinse off with warm water. Store out of the reach of children. It should keep for 1-2 years.
No idea as just lifted this from a website but might be worth trying. As they always say - Test on a small inconspicuous area before use to ensure colour fastness