Are you actually sure that this isn't a case of a bad MB dealer fucking up and then using "Tampered Mileage" as an excuse for them screwing up his ECU or whatever Module ?
Wasn't a Navi Update was it and now the whole COMAND /Dash etc is screwed up, I've had plenty folks who that's happened to by Main Dealerships, I wouldn't let them near mine, did the update myself
Plenty of options here to get to the bottom of it
This age of MB will store it's mileage, (well actually Km), travelled in many other Modules as well as the Cluster and ECU, the Navi HDD is a good place to start, hopefully the villain wasn't clued up enough to delete that data
Get the car interrogated by an Indie MB Specialist, or a trustworthy dealer who has bang up to date SDS, you'd be surprised at what info I can access, like exactly how many Km the car had done when an event or fault happened etc etc etc ................
Does this car have COMAND with Mercedes ME, if so the figures will likely be stored on the MB cloud, and I think this is a good enough reason to justify MB circumventing Data Protection and thus releasing the data
A friendly Service Manager would go a long way to helping here
It could well take a few hours to dig through it all but may well be worth it.
It is a brave or extremely dumb arsed man who would tamper with the Mileage on a recent MB vehicle
HTH