Navistar uses Blue Dimond Logic electronics. Navistar pushed for that in the F's. The early F's (03 and early 04's) had lots of calibration problems due to problems converting Blue Dimond peramiters to Ford. Thus all the reflashes on the early ones for drivability problems. Now Ford is just tweeking smaller issues. I have talked to afew school bus guys. They say the same as mschn99 same leaks, less drivability and way fewer headgaskets.
It is my guess thet the headgaskets are not as big of problem as they think. I think the engine is prone to hot spots, mainly in the egr cooler. Trucks that have lower egt's have fewer problems with blowing chow. The new recall for the degas bottle label is to lower the coolant level in the degas bottle. This gives the coolant room to expand as it get hot. Time will tell.