I just got handed a different work vehicle, a 2005 QX56 with 155,000 miles. We had it in to the local Infiniti dealer for some work and the service tech told my colleague (in a bit of a whisper) that the vehicle had an exhaust problem which would be prohibitively expensive to fix but if it was not fixed it would lead to a blown engine in another 10-15,000 miles.
I was not there so this is second hand but I can't think of how this could happen, unless the baffling collapsed and restricted flow so much that the exhaust gases couldn't escape. I also can't understand how it could be that expensive to fix. I've searched the site but can't find this issue discussed.