You can use acetone or paint thinner. Ensure to follow manufacturers safety recommendations for eyes, skin, respiratory, etc. when utilizing these products. Place a small amount on a rag or paper towel and begin rubbing the surface of the paint gently until you can see the lexan. Make sure to do a test spot first and see how the shell reacts to the chemical. Always flush the area with soap and water when done. Keep in mind these chemicals can haze the lexan, so use sparingly. Good luck.