I thought I got rid of this a couple months ago when my windshield was covered and now it's back...I use rain x on my windshield and not sure if that's affecting it.
On the windshield (top) the half moon of smeer never goes away no matter what. The bottom is the hood where the water normally runs down after wash. Not sure if my solvent is staining it or a chemical reaction with the rain x from the windshield. Still have winter fluid in the resevoir.