Upon undergoing state inspection, it was discovered that the passenger side upper strut mount had failed completely. If the car is jacked up, the strut drops out of the mount. This could have led to a catastrophic failure during operation. My wife is the primary driver and does not drive it hard. The car has been in no accidents (other than a rear fender bender in a parking lot). I have found a Technical Service Bulletin for 2014-2015 CTS (Bulletin # PI1510A dated Sept 14, 2016) "Popping Noise from Front of Vehicle When Travelling Over Bumps". We never noticed such noise but the bulletin ascribes the noise to the possibility of "the front strut mount being torn...". My problem is clearly what is described in the bulletin, taken to the extreme of completely failure of the strut mount.
The dealer wants me to pay $1258 to replace the mount and the strut (which they say is damaged, too). I showed them the TSB, which they claim does not exist in their computer system. I showed a printed copy of it to the service adviser and he simply said "I don't know where you got that, but no such TSB exists". He acknowledged that a GM TSB looks just like what I printed out. I told him I had no way of creating a GM TSB, therefore this muse be legit. I am not sure if the TSB obligates them to cover the repair under special warranty.
Any Advice Please?