aluminum Flex fans are good to 6000 after that they usually come out the hood. Front or rear mount calipers? Are the plastic dust shields in place behind the strut rods. Just some things to check. Single piston calipers always have rotor contact and drag. The 4 piston calipers do not the free wheel when released. Drive a car in traffic and you will suck in brake dust from other cars also. There is a list of things it could be . Start doing test but I find it hard to believe its from the head gasket.
