Rear differential was deemed defective during state inspection and a safety issue if not replaced. The rear differential case was cracking and pulling apart. The cause for the crack was communicated as corrosion from road salt and winter weather exposure. I live in the North East! I call defect. When researching this issue online, it is a commonly reported issue with Jeep owners and an obvious manufacturer defect. Jeep Cherokee owners have experienced cracks in the rear differential casing and discussions suggest that these cracks are due to manufacturing defects or bad casting.