I agree with Jim that the second cracked bell housing is talking pretty loud that someone not something is going on.
Check the ratios, pull the covers do the math, ring gear divided by pinion. Verify before having a cow.
So far you have been very calm about the whole thing.
Next is to bring it to a shop that has a stellar rep and pay what they want to go through it. Sounds like the jeep has some good stuff ARBs SYE kits...you have good money going for some bad work. Nip that.

SD