Thanks, I needed to read the last part to clam myself down.
I did retry the polar seal on a small area of the boot lid but no joy… I’m leaning towards just putting it to the back of my mind and hoping it comes out in the next wash in a months time.
The clay bar should be safe. Go with a name brand clay bar package, complete with spray lubricant, and if it was my Tesla, I’d only use a new clay bar, not one that had been used previously or on another car. The clay is supposed to remove the surface contaminants without abrading the clear. I’ve used clay bars and they works well, I have not used them for water spots though. If you touch a sandy or dirty area of the car or if you drop the clay bar, throw it away right then, don’t try to use it. If it gets grit in it it will scratch. I’d use it on a small area and make sure it works and gives you the finish you expect. The surface should be washed and clean before the clay bar is used. The general idea is that the clay bar is sticky. It slides over the paint but surface grub sticks to the bar and is lifted clean. I believe some clay bars can be minimally abrasive, that’s why I’d go with a name brand.
A clay bar should leave a slick absolutely clean surface.
It’s possible the droplet isn’t a calcium residue but an etch of the paint. If it is calcium, it will come off with a bit of diluted vinegar on a microfiber cloth. If it’s an etch it’ll need to be rubbed out. Mild machine rubbing compound applied by hand is very safe and will be effective if it is indeed an etch.
So I’d start with new microfiber and distilled water. If spots remain, then dilute vinegar and apply with microfiber, rub then rinse right away. Next I’d use a new clay bar. If spots remain I’d then go with a very mild rubbing compound, they’re usually labeled ”polish” but they are still abrasive, absolutely minimally abrasive but abrasive nonetheless. It can be confusing, some manufacturers will label wax products ”polish”. Some manufacturers make a “cleaner wax”, those contain an abrasive as well so I wouldn’t use those unless you have experience with that particular product. At any point you can try an automotive wax or a sealant and see if the spots remain.
I’m just an owner, I don’t do paint for a living, so weigh this against others advice. If there are paint professionals, I invite them to weigh in. If you see something that needs changing jump right in. The important thing here is accurate information. But if you do jump in to alter, correct, or adjust what I’ve said, please back it up with an explanation.
The thing that troubles me a little is the Polar Seal admonition about applying to the windshield. Does it damage the glass, does it result in a coating that affects seeing, does it cause the wipers to chatter, it would be nice to know exactly what they are thinking.
Good luck.