Fuel Filler Corrosion
The filler neck on on my 2001 (it has 107,000 miles on it today) was corrosion-free up until about the time that they reformulated the diesel fuel for the 2007 model years. I'm not a chemist, but I would say that there is something in the new formula that is causing the corrosion.
I haven't noticed anything unusual in the fuel filter at the regular 15k replacement intervals, but I am keeping my eyes on it closely. Up to this point, the corrosion appears to be the garden variety grey oxidization that you can get on aluminum. While it isn't flaking or anything, if you wipe your finger across it it will rub off on your finger.
On a similar note, there are some issues over at Ford with corrosion on the inside of the fuel tanks of Superdutys, and in fact, it is so bad in some cases that the inside of the tanks are delaminating and beginning to cause downstream fuel filter and injector problems. They are blaming biodiesel as the cause, but I can tell you that the diesel that goes in my rig has never been anything but straight-up dino variety, so I know that at least in my case, biodiesel is not causing my problem.
\'01 Chevrolet 4x4 2500HD SB EC Silverado LT, D/A, black on black, Line-X spray-on bedliner, Fumoto oil drain plug, TTT-Mirror 1020 tow mirrors, Nokia CARK-91US cell phone kit, Tekonsha Prodigy electric brake controller, Boston Acoustics RC-620 front door speakers