I popped off my headlight lens to clean it today. First, I just rubbed a couple fingers on the inside of the lens the see how easy the film would come off.
You can see it actually rubbed off really easy.
So I stuffed a dry, lint free towel inside the lens and tried to scrub the back using a bamboo rod (happened to have a bamboo back scratcher on my workbench
). This actually got the inside of the lens pretty clean but I decided to go a little extra by spraying some RainX 2-in-1 glass cleaner on the towel and repeating the process. The lens is lead crystal glass so the RainX was safe.
Here are before and after pics.