[Achilles]

Disc rotors (Fremex Carbon + ) were changed last November 2016, already hit 15,000kms, mostly highway drive. I recently had a weird sound (EEeeeeEEEeeeee) while slowing down or when I press brakes slowly.I noticed the rear right rotor is uneven, especially the outer is rusted, forming a rough surface. Is the pad becoming thinner?

 

[DEVOURS]

Remember that the rears do not apply right away when compared to the fronts and the fronts do most of the stopping and this makes rust in the rear if your apply softly (like I often do).
The rear pads are probably being eaten up when you see that rough and dark area. You park the B for a week and if there's any rain,..you're basically screwed..

I've tried a lot of tricks to get rid of that rust (I've explained them in the past here), like finding a steep hill and racing down backwards and jamming on the brakes to apply more to the rear in hoping to get rid of the rear rust..

Dangerous but maybe a bit effective..

In the winter I do the same backwards and the fronts lock up and slide in the ice and snow and the rears slowly apply and clean up. Crazy way to keep our B on the road and with clean the rear brake rotors..

MB says that there is no proportioning valve to play with..so we're basically screwed with these brakes in this "quality MB car"..

 

[Achilles]

So sad to know about this. So should I be changing the rotor? But rotor is clean for the other side, rear left. Is it rotor becoming thinner or the pad is wear out?