Carrier/rack problems of the 2016 Mercedes Benz S550

I woke up one morning and was astounded to find a long diagonal crack across the panoramic sunroof of my 2016 mercedes-benz S550. I contacted mercedes and was told to bring the car to a dealership for evaluation to determine whether this was due to outside influence or a manufacturer's defect. They determined that it was a "stress crack" and stuck me with a bill for $13,000. This is a 2016 model car with 50k miles on it with a sunroof that spontaneously cracked. What if my wife and young children were in the car when it started to crack? the response from mercedes is unacceptable. This is a very dangerous manufacturer's defect which must be addressed before someone gets seriously hurt.