Unlike porsche, AMG will warrantee the BS even if you track it. The 6.3 is really understressed as others have mentioned so I don't think the fact that it was driven by the dealers son would wear it out. Two schools of thought on break in, A. Drive it like you stole it. B. Follow the mfg advise. I don't think we've seen any adverse consequenses on either way. The real reason for careful breakin is not the engine, but the rear axle.
For a few lucky owners who took factory delivery and raced their cars in the AMG Trophy cup, the factory insisted that the cars be broken in by their test drivers.
A number of owners have driven their cars in various forms of motor racing without any side effects. They told me at the factory, go ahead try and break it.
If you looking for a new one, Laguna Hills, CA has a Mars red with only delievey miles.
I think they want over a hundred.
Jimmy