As a long time GM driver I've been aware of this problem for years, but have always dodged the bullet except for a 90 Grand Prix. It was almost impossible to find a picture of these things:
http://www.dieselplace.com/forum/sho...light=15765007
It's more of a fender liner than a mudflap. I'm not convinced that the average driver needs these, but I would sure get them if I had a problem.
The 90 Grand Prix was the first mass produced GM with rear disks. If I remember right, there was no recall, but I got the first brake job on GM under the warranty. Of course that just fixed the brakes not the cause which was mostly corrosion due to salt spray. The fronts were never a problem, but wore faster because the rear never worked properly. The ultimate solution for me--and my happy mechanic--was an annual "brake service" on the rear brakes to clean up and lubricate the calipers and bolts. GM eventually went back to rear drums and then did the same on the 04 or 05 Silverado although the HDs always had rear disks.
I used my 01 Silverado as a daily (and only vehicle) driver and never had a problem with rear disks. That included lots of gravel miles on the Alaska and Dempster Hwys. As I understand it, the problems is small stones getting trapped between the rotor and the shield to the inside of the rotor. Grit can also get under the pads and of course salt creates all its own problems. But I've always had front mudflaps (rear also) and I think they would help quite a bit. Interesting thing is my 77 F150 had a similar fender liner on the front rear fender, but not with the flap hanging down. I believe the new 07 and up GMs also have more of fender liner to the front of the rear wheel.
Henry