I know off topic, but I was getting a bit of 2-1 slam on my E70 N52 with the ZF trans and cleaning the vanos screens cured it, so maybe sometimes the engine not running properly could have something to do with it.

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