I think all C5s have brake dust, etc. buildup on the very rear of the car - it's due to the aerodynamics of the car. If you're talking about the wheel wells specifically, then no, I don't have problems with that.:wavey
I notice brake dust on the rear fascia behind the rear wheels but only if I am driving hard. Otherwise no issues. Now the rear of the car is different. That attracts dust/dirt. So much so I wash the whole car only to clean the rear.......
Are you sure its not Tire shine that has been thrown from your tire onto the car? This is a common problem with many Tire Shines
On CorvetteForum.com Their are two great reviews of "Looks Wet No Mess" Tire Shine. Both reviews mention that the product doesn't Fling off onto your car.