NHTSA Complaint #11487294 — 2014 MERCEDES-BENZ C300

I purchased my car one year ago from a Mercedes dealership - 8/31/2021. I brought it in for service at the same dealership a week ago and they told me the rear subframe rusted from the inside out and it FAILED inspection. The parts are $5,100 and not available until some time in Q1 2023. There is no way a car rusts from the INSIDE OUT in one year. I have another vehicle in the same driveway, same everything and there is no rust anywhere. We have had all of our cars at least 10 years. This was a "new" car for us. MBUSA said they could do nothing because I own the car and didn't get financing from them. My dealership so far is not helpful. My service guy (he has been for 10 years) says this is common?? My client (a different car manufacturer) says it is not and it is terrible. I don't know why it rusted but this is a defect in the car because we didn't flood it. It's dangerous.