This issue has come up a lot on this forum...so far the jury is out though...a few K&N users have said there are no adverse issues with their MBs.

There is also another oil thread with regards to using Fram oil fiters on MBs...kinda the same tone...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car