Had mine at the dealer 3 times and finally got them to call GM and convince them of replacing the entire carriage. They were originally going to try and replace the clutch packs but found that the gears inside the rear diff were totally worn out at 26k miles. I imagine this differential will last just long enough to put me past my factory warranty. This is the prettiest car I've ever owned, but it's absolutely the worst design and build quality I've ever had by a factor of ten. So far, the steering gears replaced, belt tensioner replaced, extra padding added to driver seat due leather stretching and I only weigh 167 lbs, multiple trips for rear diff with eventual complete replacement, fix leaks around windows due to faulty gasket install at factory, undetermined rattling noise above glove box, and undetermined reason for noisy AC compressor. It's pretty insane given this car is so new and so well taken care of by the owner. I'm likely going to sell it soon before it falls apart.