more than likely it's fall out which is normal if you dont wax your car that often. brake dust sits on the paint surface and rusts. Will need an acid bath and an immediate coat of wax.
I'd say the 30,000k trans flush is about right as benfolio said they usually turn up dirty right around there the transfer case and diff seems way premature though, things are regional as well even oil changes. mazda recommends 7500 miles but even at 5000 the oil is black as night personally i'd...