You never know how much melamine and lead and other suff like metal can be in that plastic. They could have rearranged the atoms to cloak it. Don't lick it to clean it I checked out and that lens is made in Hong Kong. Never knew that. Been there three times and one of our favourite cities. It has been quite a few years since out last visit.
Have you tried running it through something like Photo AI? I kept Topaz Sharpen AI around for these moments. All this new AI stuff is saving me thousands in lens purchases. If I won a lottery I'd get me an RF600 f/4 but I no longer covet it.