[4x4]

Doubt they are stainless steel, more likely anodised aluminium so almost impossible to get back to looking new. Don't be tempted to remove the anodising with abrasive cleaners as this would leave the aluminium exposed to the elements and it can/will deteriorate. Polish with a good quality car polish that contains a light cutting compound and wax is about as much as you can do, it will make a slight difference but won't make it perfect.