After a long braking or a very hard braking the the pads get very hot. Very hot.
You screech to a halt at a light and hold your foot on the brakes. The heat from the pads concentrate the heat in the disks at one spot, the disk expands at that point. Never to return to the exact original thickness. (you can feel 2 thou)
When driving hard try to stop a little back from the line and let the car creep a head slowly. That will help to distribute pad heat around the disk.

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1984 300SD turbo 126
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God made me an atheist and who am I to question His wisdom