Other than the rotors, the other possibility could be control arm bushings. Have you at any time had some clear mineral oil leak, not much, just drips, but they disappeared after a while? If you did, that was the hydraulic oil from the control arm bushing. When that casing inside the bushing breaks, the little amount of oil inside leaks out, then it would still go for some time until one of the symptoms show...which is what you described when braking.
So, just be prepared as your dealer might just recommend replacing the rotors, and then find out later that they were not the cause! All at your expense of course! And they'll tell you, "Well, the rotors need to be replaced anyway..."
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2012 Porsche 911 GTS
2008 Ford F150 Foose Edition
2010 VW Touareg
Gone...2002 Porsche 911 C4S
Gone...2000 BMW 540i
Gone...1995 BMW 540i