Headlight cover restoration

Mopar Tim's got it right. when "plastic" (polycarbonate) headlamp lenses are yellowed or clouded or fogged, it's time to replace the lamps with new original-equipment ones. There are various polishing/restoration kits and techniques on the market, none of which will do anything but postpone your need to install new headlamps because what you are doing in "polishing" the headlamps is scrubbing off the anti-UV/anti-scratch hardcoat that was applied and crosslink-cured under cleanroom conditions when the lamps were manufactured. With this coating gone, the degradation will come back faster and worse than before. Many of the kits contain what they claim to be a coating, lotion, wax, protectant, sunscreen or other such goop; none of these does anything to slow or stop the degradation. There is no field-applicable coating that can come even a little bit close to duplicating the factory coating's performance (which itself is inadequate to the task, as a walk through any parking lot shows -- the regulations are too lax), but if what you need is to buy yourself some time, use UV-stable urethane spar varnish (link is to how-to thread).

Also, a headlamp that is not in as-new condition is not worth using. Optical degradation of the reflector is grossly advanced well before you can see it with the naked eye; by the time it's progressed far enough to be described as "just a little imperfect" the lamp is dead. Remember, even the most costly, beautiful show chrome (the kind that looks a mile deep) is only 67% reflective, not nearly enough for optical purposes. An as-new headlamp reflector is over 99% reflective. The takeaway message here is that even if the reflector looks OK, its optical efficiency is way down if it's got some years on it.

Replacement headlamps need to be original-equipment items (automaker's own brand, genuine parts) because all(!) of the aftermarket off-brand items (TYC, Depo, DJAuto, Eagle Eye, Helix, etc.) are garbage, despite spurious claims of "OEM quality", "SAE/DOT approved", "CAPA certified", etc. This is worth a careful look at your present headlamps, too, in case the car received aftermarket replacement headlamps sometime in the past.