certainly on a MKII the headlights can be polished in situ but you do need to remove the front bumper which is an easy task.
Various headlight cleaning kits, 3M at about £20 is a good kit, I have a sealey kit but not yet used it

macafee2

Once cleaned, I apply a thin film of ACF-50 grease to brake pipes and metal connections. ;) Never failed me yet. If it works on aircraft carriers ......:shrug:The ACF-50 spray is great for rad cores, aluminium and aircon parts but do NOT get it anywhere near belts or brake friction parts as it is a lubricant.