Does he have any other mods? How big is his lift and was it done by someone experienced? Can you be more specific as to how it continues to break, i.e. is it getting sheared off or is being damaged from inside the TC? Theres really not to much going on inside the tailhousing itself. I know the bearing that shaft rest on can be tempermental if the driveshaft angle is to sharp, but with our trucks thats really hard to do. Its really common in Jeeps because their so short.
There's allot of smart folks in here, so tell your buddy to keep his head held high. Im sure someone here has the answer.