I live in a maritime province and the salt air takes it's toll. I went to a local marine shop and found a strongly recommended product for protecting metal.
Thousands of picky sailor types can't be wrong.
The product is this:
COLLINITE's #850 LIQUID METAL WAX Pint
The easy to use liquid metal wax cleans and protects chrome, aluminum, copper, brass and stainless steel in one easy step.
Will safely remove rust and salt deposits while protecting marine fittings/accessories and car, truck, and motorcycle metal finishes.
Contains neither strong acid, nor harsh alkali.
They use it on their sail boat metal parts (mostly brass, aluminum and stainless). I figured it would be great for a polished valve cover.
Here is a before and after shot of a quick application on a new (but used) wheel spinner I recently picked up. I think any wax would have done the same but this stuff is supposed to protect as well.