Using toothpaste to clean your headlight covers sounds ridiculous... But it works
Apply a line of toothpaste onto the cover and spread onto the entire cover.
If your covers are very dirty (like mine were), use some type of brush to scrub the toothpaste in better after spreading.
Pour water over the cover and wipe off with other washcloth.
The ending result will amaze you. Repeat these steps the next day if you are not completely satisfied.