Here's the easier way to do it, Car Pro Iron X (other fallout removers are available, Autobrite purple rain, bilt hamber korrosol, ), still would clay after the fallout remover and tar remover if required.If you live somewhere where your car will travel by rail to get to the dealer, check for railcar brake particles stuck to the paint. These are tiny hot metal particles that come to the car in the form of sparks. They are hot enough to stick to the paint and are hard to remove. When they get wet from rain or washing, they leave rust coloured streaks.
They can be removed with a clay bar but it is a time consuming job.