Your dealer is "denying the obvious". If a disk has to be replaced it’s because its surface is damaged. Since the pads interface INTIMATELY with the disk any damage to the disk WILL damage the pads. Replacing the disk then allows the damaged, unevenly worn pads to damage the new disk. Your ineffectual braking subsequent to disk replacement was due to the unevenly worn pads not making full contact with the new disk and damaging the new disk as they wore the disk to match their damaged surface.

If the dealer simply doesn't get it, you NEED to find another dealer because this brake problem is just symptomatic of MANY other matters they won't get!

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A good pessimist is never dissapointed!