think most are alloy so i guess some kind of suitable metal polish paste to cut into all the crud that covers an intercooler. its like white corroding powdery stuff. mines a bit mucky and id like to give it a clean but its such an arse to remove the remove the bumper just to clean it so like you i'll wait until a job requires its removal. mite as well clean the two hoses either side whilst youre at it.....
auto glym do a metal polish. Brasso has that polish for silverware-never tried it though.....