I know this is an old thread, but wanted to share my 2 cents. I've tried the 3M kit, and it does work. But I found that it will fog up again over time. I've heard that this is because the protective coating has worn off, which is the reason your headlight cover got oxidized/fogged up in the first place.
I found using using Flitz metal polish periodically after helps. I wouldn't use it right after using the 3M kit, but a couple months after or when you notice it starting to fog up again. I really like Flitz polish, and can't recommend it enough. It works great for lightly oxidized clear plastics, and less prone to scratch painted surfaces. You don't have to tape off the headlight, as long as you're careful.
I've heard applying a protective transparent clear headlight cover or a clear bra after cleaning/clearing up the oxidation works, but have yet to try it myself. I would like to know if anyone has tried it.
Also heard of another method is applying a clear coat after polish. But, you have to be very careful to evenly apply the clear coat, though.