G3 compound and T-cut etc is what people use to take faint scratches and over spray or sun faded paint to bring up the paint smooth and shiny before polishing on car bodywork , that is what I used (T-cut rubbing compound) then polished it with mer polish which is a finer rubbing compound with wax added to it to make the headlamp clear to remove the faded UV damage , then sealed it in with no1 supergloss , but I have bought some clear none yellowing from UV clear cote lacquer if they fade again so that its a permanent fix . I am sure the metal polish you have will do the job but it may need 2 or 3 attempts depending how quick it can cut through the haze .