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To get rid of the water spots, use isopropyl alcohol (rubbing alcohol) on a rag. Then clean with a window cleaner.
Be VERY careful in this area with rubbing alcohol. It messed up an area of the paint on the underside of my hatch when I tried it to remove something sticky. Luckily it it a hard area to see.
I know not everyone has access to one but my house has a water softener so I ran a dedicated line in my garage and have a hose reel in the garage that I use to wash all my cars if I go that route, typically I just use a 'waterless' wash but still us the soft water with it. Either way there is never a water drop that can be seen once dry w/ the soft water. I remember on my last Vette which was black and I did not have the soft water, it was a project cleaning the hard water spots in door sills and under hatch and hood once they dried.
I always use a quick detailer just as you would outside the car to clean up the paint in those areas and on my Stingray, I use the detailer on the black plastic under the hatch as well as the plastic trim inside the car and its worked great. I also use a spritz of it on the inside of the windows on a separate microfiber cloth and have been doing that for over 10 years on all my cars and it also works great. Works as good as Windex. just my preference for how I do things as I have a bad case of OCD.
i use the Adams greenish - milky color interior detailing stuff. seems to work well for me. that flat black area always seemed to have some streaking or spotting on it
"Underhood Spray" from www.griotsgarage.com works well and look nice without runs, etc. Some things will desolve and smear the black paint.
Have you heard if this is a factory defect? I ran into the same thing with my New 2017 Stingray. I've never had a car that I cleaned and the paint came off! I'm going to go down to the dealer Saturday and I only have 3000 miles on my car.