I did a search on "remove headlight" without the "", came up with 17 results and a plethora of info on the covers.. I even used the search the title of your thread using the title search feature next to the title input field when you start a thead, it showed approximately 7 results, one was titled "Crazing" which may fit your problem.

Make sure it is on the inside as there has been some documentation of the top outer surface hazing.. Some have been replaced and some have been polished.