Dust will leak into the vehicle where water will not. This happens particularly in the lower portion of the interior. Forward motion of the vehicle creates a slight vacuum which pulls air and dust inside of the vehicle.
Perform the following steps in order to determine the location of dust leaks inside a vehicle:
Dust in the shape of a small cone or slit will usually be found at the point of leakage.
Ensure that the sealing of leaks is done with an air-drying, flexible body sealing compound.