Time required:
10 minutes per headlight
Materials:
Isopropal alcohol
Cotton tip swabs / Q-Tips
Compressed air
Reflector cleaning is not part of typical maintenance. You could damage your headlights following these steps but this is what worked for me.
While performing an amberdectomy a thin layer of plastic soot blanketed my turn signal reflectors and diminished light output. This was primarily visible on the spherical reflector but also on adjacent flat mirrored surfaces.
Step 1: Inspect the reflector
I assume you know how to remove the headlight assembly. If not please consult your owner's manual which details the process. Remove the turn signal bulb; the reflectors are visible inside. Use a strong light source to examine the reflector from different angles. In my case the surface looked cloudy from some angles but not others.
Step 2: Cleaning
First a note about materials. At first I tried distilled water since that poses the least chance of harming the delicate surface. It appeared to clean the reflector but once dry the haze returned. At this point I switched to isopropal alcohol. I also tried two different types of cotton swabs. The first was a general cleaning swab from a chemical supply company. These had a tightly wound cotton surface. Ultimately I found common Q-Tips work much better. The cotton is wound looser so be careful not to snag it on any edges along the reflector. When finished use fine tweezers to remove any cotton strands.
Dip the Q-Tip in alcohol and gently draw across the reflector to remove the surface film. You may need to bend the swab at an angle to reach inside the concentric reflector grooves. Keep the cotton wet with alcohol and discard when visibly dirty. Q-Tips are inexpensive so use them liberally. Repeat the same procedure on the three flat reflective surfaces.
When done cleaning, use the can of compressed air to dry residual alcohol. This may sound silly, but first practice with the air against your hand. Inside the can is a cold liquid and you do not want this expelled all over the clean surfaces. It helps to use short bursts of air, and before each use, test it against your hand until satisfied the air is dry.
And with that you are done. Reinspect the reflector, install the bulb, mount the headlight, and test.