During the last week of February we responded to a car fire on the highway. Nothing too difficult, done a bunch of them. What makes this one memorable is that the 4X4 transfer case (located on the rear of the transmission) exploded sending fragments over 50 feet away. All of these types of transfer cases are vented in order to release pressure during normal operations. Apparently the pressure increased too fast for the vent or seals causing the case to explode. The manufacturer recommends using automatic transmission fluid in the transfer cases. Unknown what was in there. A hint may be that the vehicle was on it's way to the auction from an used car dealer. Used car dealers have been known to "add" things to oils in order to make them stop leaking. No proof here though. So, lessons learned: watch out for traffic, tires, bumpers, cargos, and transfer cases. Added is a picture of the fragment found by the pump panel.