Hi folks

My Audi S5 is at the dealership cause it had problems with the alternator. That is covered by warranty. The dealership now called me and they told me that while repairing they noticed that my carrier lock is broken. And they said this has to be fixed as it is a safety problem. They estimated 8 hours of work time to fix that, and I have to pay for it cause they said this part is not covered by warranty. Furthermore they said this only brakes when the car bumps on the street, which I never noticed that I did. I will definetly have a look for myself and check if there are any traces of my car hitting the ground. But that all sounds very strange. My car has only 17k miles and I get the feeling that either they broke it or it was a material issue.
So my question to you professionals is: Does it really take 8 hours to exchange the lock carrier? Can a lock carrier really brake that easily?

Thank you guys so much up front for your help! Much appreciated