About the rotors, they are corroding internally. The ribs separating the two sides are there for cooling, they become as hot as the rest of the rotor during braking. Unlike the swept surface, however, they aren't cleaned off by the pads, so they rust.

I have never heard of the rotor failing because of corrosion, but I have to believe that it is possible. Consider buying a new set of rotors at your next pad replacement, or sooner for peace of mind.

Tom

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