Thank you and sorry to disappoint but while I work on older MB cars a lot, I'm not much good w newer stuff that needs software to diagnose.
My suggestion was to find a dealer that you can lean on. The emissions system should not be failing at that low mileage or that close to warranty ending. I've actually had decent luck w both Mercedes and BMW getting things fixed or at least partially covered out of warranty.
You need to find a sympathetic ear at the dealership, it will probably be a service manager or a long time service writer who will plead your case to whomever they report to at Mercedes-Benz.
Don't get angry w them, no matter how frustrating the situation. It just gives them an excuse to not help you. You need to approach it as a loyal MB owner who was considering buying a new one soon but you're having a little trepidation with this emissions system failure at 85k miles. That you otherwise really love their cars, that you've always thought that they were built like tanks, etc...
If you can't keep a straight face while saying the last one, maybe skip it.
The people at Mercedes have a lot of power to approve things like this, (or not), I've always had the impression that they can do what they want. If it's framed properly, i.e. keeping a customer from going Lexus next time, their JD Powers numbers, etc., good things can happen.
Best of luck w it.