Differential Unit problems of the 2009 Cadillac CTS

The rear differential routinely makes loud grinding and clunking noises when making slow turns at parking lot speeds when cool and just starting to be operated. This problems was been in for service 3 times and the dealer states it is normal and an expected thing that may occur. I disagree, grinding gears and/or clutches are not normal or safe. My car was purchased new on 10/30/09 1st service came on 10/25/13 at 36,605 miles the problem was described at the service appt to "diagnose rubbing noise when making slow sharp turns, goes away after warmed up. Noise comes from rear of vehicle. " the resolution at the time was to do "as per document #3402587 flushed gear oil from rear diff and replaced with an updated fluid. 2nd service came on 3/21/17 at 64,269 miles the problem was described at the service appt to "diagnose gravely grinding sound from rear of vehicle when making tight turns at parking speeds. Also noticeable 25-30 mph. " the diagnosis and resolution this time was again "test drove for grinding noise while making tight turns. Was able to duplicate concern found coming from rear diff. Per doc id 4013532 recommend servicing rear diff with new fluid. New fluid has additive that will last longer and does not break down over time. Serviced rear diff and test drove found noise went away, no other repair needed. " 3rd service came at 6/18/18, at 71,678 miles. The car is presently in the shop for diagnosis and service. This is only 7,396 miles since the prior service. The problem was described as "inspect for gravely sound when making turns **rear diff service done for this ro#394816 3/22/17 #881. " the problem I have with this is that this is not a normal and expected problem and could be very dangerous if the rear transaxle fails while driving at speed due to a gear or clutch failure. Gm knows of this problem based on the fact they have 2+ bull.

I was driving my 09 Cts-4 w/ 20,000 miles on 12-12-09 @ 40 mph when I heard a loud boom from the rear and the rear wheels locked. This caused a huge jerk and several skips on the road before coming to rest after a 150 ft skid (paced off skid marks) . When I tried to drive the car from it's stuck position from the middle of the road, the exact same thing occurred @ 5 mph. The car was towed to a dealer. Gm authorized the dealer to replace the rear differential assembly under warranty sight unseen. The dealer did not even remove the differential first to determine the damage or diagnose the cause. The service manager said there was no sign of fluid leakage and that the differential was full of fluid when it was removed. The differential has been replaced and there has been no problem since. Fortunately the car did not skid off the road. Had other cars been on the road, a crash would have occurred.