When I was shopping for my E320 Cabriolet, there was one thing every car I examined had in common: they had all spent time in Florida. We're talking about over 10 cars, so this was more than just a coincidence. It was clear to me that these cars have quite a following among Floridians.
What's my point? Spending time in Florida means a car has likely spent time by the water. And when a car has lived by the ocean, it usually has the water spots to show for it.
A trained eye will detect my own car's seaside history. The factory paint is quite good, but look closely at the windshield and you'll see that the car suffers from water spots on the glass and the anodized trim surrounding the windshield. Also, the rear view mirrors on either side have very noticeable water spots. In fact, these mineral deposits on the glass were so bad in direct sunlight that it could be hard to see out of mirrors at times since the mirrors and the door glass both have water spots.
I tried three different solutions. First, I tried vinegar. I removed the insert for the rear-view mirror and soaked it in vinegar for a couple of days. No effect whatsoever.
Next I tried soaking the glass in CLR. (The bottle warned against prolonged exposure, so I only soaked the glass for half an hour or so.) Again, no effect. I tried CLR on the front windshield and its trim and I did have modest success. It reduced the water spots on the trim. Oh, they're still there alright, but they are less obvious.
Finally, I used Bar Keepers Friend. This was the ticket. After applying the powder to a wet sponge and gently rubbing it into the surface of the glass, I can see again. The water spots are now gone thanks to the oxalic acid in this powdery cleaner.
I haven't used it on the anodized trim yet, but I will test it first to see if it removes the color.
Bar Keepers Friend, aka "A124 Cabriolet Owner's Friend."