I've seen more than my fair share of rotors that were bad right out of the box. Make sure the shop tests run-out on the new/machined rotor.

Of course, crappy rotors will warp quick as well, due to the inferior metallurgy.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.