Broken Xfer case adapter

[Keith 3267]

I recently bought (Oct, 2017) a 2007 Silverado Classic 1500 Z71.  It started making a loud knocking noise and dripping a lot of fluid from underneath.  I had it towed home.  The noise was the rear U-joint of the front drive shaft hitting a cross member, the fluid was ATF.  I discovered that the adapter between the transfer case and the transmission was cracked clear around and the transfer case had drooped down tot he cross member.  The truck was driven into a parking lot so the transmission and 2wd of the transfer case were still working and the transfer case shifted into neutral for the tow truck.  Loss of ATF would have prevented it from going much further though.

 

I have removed the transfer case and drive shafts and ordered a new adapter.  I found that the front U-joint on the rear drive shaft has lost all its needle bearing on two opposing caps.  There was a slight vibration when driving the truck but I thought that it could be due to the fact that none of the wheels had any balancing weights on them.  All the tires are fairly new though.  I bought the truck from an old man, usually they are a good source for used vehicles because they maintain them better and drive them easier.  After I bought it, he told me that he bought the truck for his son to use but now his son has graduated from HS and needed something with better gas mileage to go to college with.  Big red flag I wish I had known about.  This truck has been abused.  I can see signs that it had been used for "mudding".

 

My question is, is it a common thing for the adapter case to crack like that and what would have caused it to crack?  BTW, there was no skid plate under the transfer case.  Could the vibration from the U-joint contributed?  I did not test all modes of the electric shift transfer case but it did work fine in 2wd and auto 4wd.  I did not try 4wd hi or low.  Could there be something wrong with the transfer case that caused this?