First let me say, I realize you can buy headlight restoration kits that work just as well. I've used the 3M kit before and it worked well on my old car. But they are usually $15+, and one time use. I had most of the supplies already to do this, and can repeat in the future without having to buy anything. I figured I would just show people another option.
My 2008 E92 335i had developed what looked like eyebrows, except not the cool kind. They were oxidation eyebrows!
This headlight not quite as bad, but still ugly:
I tried rubbing some Meguiars PlastX using just a terry towel, but it only cleaned them a little bit. This was going to require sanding.
-Terry Towels, lots of them
-600 grit sandpaper (1 sheet cut into 1/4ths. I used a single 1/4th sheet per headlight)
-1200 grit sandpaper (cut same way)
-2000 grit sandpaper (cut same way)
-Spray bottle filled with water
-Meguiars PlastX (or any other oxidation remover/headlight restorer, 3M rubbing compound, etc)
-Porter Cable Orbital Polisher
-Lake Country White Foam Pad
-Lake Country Orange Foam Pad (white turned out to not be enough cutting power)
-Blue Painters tape
Start by taping everything off. Don't want to damage your paint! I did this before sanding, then cleaned the tape off after sanding, and re taped prior to buffing
When everything is taped off, you are ready for your first wet sanding. Spray the headlight liberally with water. Using the 600 grit sandpaper, sand the headlight as evenly as you can. I really focused on the "eyebrow" obviously, but overall I tried to sand the rest of the headlight evenly as well as to not have any non-uniform scratching. I spent about 5 minutes per headlight with this step, making sure to spray water throughout the process to keep the headlight wet. When you finish sanding, spray the headlight off and wipe it with a towel, to check how uniform your now hazy/scratched headlight is. Don't be afraid, it won't look good (but will be VERY smooth). This completely removed the eyebrow, but hazed up the entire headlight. Mine looked like this:
Repeat the sanding process, except this time using 1200 grit paper. I spent the same amount of time on this step as the 600 grit. Rinse and wipe the headlight when finished. Mine looked like this after 1200 grit (not much different, you essentially are just removing the 600 grit scratches and replacing with 1200 grit)
Move onto the 2000 grit paper. I spent more time on this step, about 8-10 minutes per headlight as to ensure I had things as evenly as I could get them and had removed all of the previous scratches. Again, make sure to use plenty of water as you are sanding. I was holding the bottle with my left hand, and sand paper in my right hand, and spraying as I sanded. Clean/wipe when finished. My headlights looked like this:
Now would be a good time to either fully wash your car, or in my case I just peeled off the tape, and rubbed the front end and headlights with a wet towel dabbed with some rubbing alcohol to remove all of the wet sand haze. Re-tape your headlights with clean painters tape. Now comes the magic part, the polishing/buffing out of all the scratches you've put into the headlight. I did this step using a Porter Cable orbital polisher with Lake Country foam cutting pads. An equally acceptable approach would be to use a drill with a wool buffer attachment. Meguiars PlastX was my compound of choice. There are probably better products such as 3M rubbing compound, but in this case I was relying on the cutting pads to do most of the work instead of the compound. I spent about 5 minutes per headlight with a white pad, which is just a very very light cut that is typically used after you have removed paint swirls and are putting on a polishing compound onto your paint. I didn't want to over buff the headlights so I started with this. As you will see, this turned out to not be enough to remove the scratches.
With my headlights still looking hazy (but at least the eyebrows were gone!) I was disappointed at this stage thinking I wasn't going to be able to remove the scratch haze, but I switched to a Lake Country Orange cutting pad instead of the white. The orange pad is typically used with a paint swirl remover, so it is capable of light cutting action. I also turned up the orbital polisher to almost full power (5/6). The results were MUCH better!!
Overall I am very pleased how it turned out. If I didn't already have a Porter Cable (that I previously bought to do a paint swirl correction when I bought the car), I would have probably just bought one of the 3M kits that uses a regular old drill. Hopefully this at least gives people another option to consider. The only thing I want to do more is I want to put a sealant on the headlights to prevent oxidation from happening frequently. I plan to use Wolfgang paint sealant 3.0 on the headlights the next time I seal my cars paint.