I used 3M Headlight kit that I picked up at WalMart for around $17. It worked pretty good. Headlights was all cloudy with a chance of meatballs. But after about 35 minutes per light it was clear as light. Now I consider this kit to be extreme, but useful because of the condition it was in. Now is there something I can do to protect it? I mean I realize it can happen again.
The problem with 3M and other sand and polish kits is that they're good at removing the original factory protective coating but don't replace it with a new one.
That original factory coating was applied for a reason. Without UV/moisture protection, your headlights will degrade quickly. Waxes will work if you keep them up, just like the wax on paint.
There are great products available to put back the protective coating, but they're not easy to get nor cheap.
The best coatings are 2k water bourne or 1 or 2k UV cured.
Have no experience with Minwax spar urethane/mineral spirits, but I do sometimes use a polyurethane based coating probably very similar to the Minwax mixture, but I only use it on acrylic such as tail lights, trun signals, emergency lights, etc. I switched to a 2k water based product some time ago and use it for most headlights but it costs about $100 for 16 oz., but only about .80 per headlight. Out exposure tests indicate it should last at least 36 months so I am warranting it for 3 years.
Sylvania makes a kit that has a 1k coating that I used once in an emergency and I believe it's the same polyurethane product we use. You might want to buy a Sylvania kit just to get the protective coating.
ray6