Maybe the seal ring gets spun at times like when the oil is thick or even gets stuck to the cam if the car is sitting for a long time and causes the wear especially since the lock portion could have sharp ends. The seal rings can't be holding the cam in place or the teflon ones would never stand up.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)