I learned the same thing but as a bonus to some body work I had done to my 6 yo car.
After repairing the side of the car, my body guy said the rest of the car (and glass) looked like crap
so he buffed out everything. I had been at the glass with vinegar, paint thinner, lacquer thinner,
razors, SOS pads...the water spots were still so bad they looked like overspray!
Sure am glad to know there is a solution to the problem
