Brake Issues with 2015 GL450

I recently purchased a CPO 2015 GL450 from a Mercedes Dealer here in CA (to remain nameless for now). Within a few weeks, I started to get a serious shimmy in the front end when braking at freeway speeds. I took the GL to a local MB dealer who told me all four rotors were warped and needed to be replaced. So, I took it back to the selling dealer and, after pointing out I had only driven less than 600 miles, they reluctantly replaced all four rotors and all brake pads.

My question is - should that have been done during the CPO inspection of the vehicle? Seems to me it should, but the dealer said the rotors were "within tolerance" when I drove it off the lot. Just looking for some perspective or someone who has had a similar experience.

Thanks.

as in sunny S.Africa, I believe most dealer have a "friend" at the CPO/MOT that let some issues slip by...

as for the warping of the discs, it could be that it was washed directly after driving. The cold water is no friendly with warm discs.