The issue rested with the steering gear - NHTSA received five complaints of failures - which was redesigned in 2005. According to the report on the matter, investigators "found evidence of broken sector shaft gear teeth and piston damage consistent with incidents of single event overload."
NHTSA investigators, however, "found no evidence of fatigue or material property defects in any of the fractures. Analysis of complaint rates by vehicle build month showed no patterns indicating potential manufacturing quality issues and no difference before and after Ford introduced design changes to the input shaft and sector shaft seals in July 2007 to address potential leak concerns," according to the report, obtained by The Detroit News.
The conclusion of this investigation doesn't just shut the door on the 2008 models, but it marks an end of investigations dating back to 1999 to 2001 model year Super Dutys, as well as 2000 and 2001 Expeditions. That investigation ended similarly, with federal investigators unable to find any defects.