I am right now getting the transfer case oil and magnet checked by a local mechanic after contacting the Ford dealer where I purchased the vehicle (not the dealer who repaired it) and finding out this problem has occurred for them several times and they have covered it under warranty. The service manager there is the nicest guy in the world and actually sounds like he knows what he is talking about.
Here is what he said:
" From the information you have given us, there is a possibility that the front differential failure you experienced was due to the shift fork in the transfer case not engaging 4WD low even though the instrument cluster icon showed the shift was complete. This can be caused by a thrust bearing cage in the transfer case breaking and the resulting debris causing the transfer case shift fork to bind between the 4WD high gear and the 4WD low gear. This essentially causes the transfer case to be in neutral. Then, with the transfer case essentially in “neutral” after shifting the transmission into drive, the accelerator is pressed. The engine free-revs and the transfer case shift fork finally engages 4WD low range. The torque amplification from the gear reduction and the elevated engine RPM from being in “neutral” combine to create an incredible amount of torque and shock to the front differential, resulting in parts escaping from the inside of the front differential.
One way you can verify our theory is to check the magnet inside of the transfer case. This will require completely draining the transfer case fluid and visually inspecting the magnet through the drain hole. The magnet is quite close to the drain hole so seeing it isn’t overly difficult. What you would be looking for are pieces of stamped metal that come from a bearing cage. They will typically be 3-8 mm long and quite slender. Sometimes the pieces have been run through gears so they may be balled up or even very flat. Keep in mind that very fine metal shavings, almost like metal dust, stuck to the magnet are very normal. We’re only looking for comparatively large pieces. If these larger pieces are present, we have a very good case that the bearing cage failure is the root cause of your front differential failure."