While I use K&N drop in filters on my Miata's (they just replace the factory paper filter with an oiled cleanable element without changing any intake components) I went through the same decision making process on the X5 as you are thinking about and elected an OEM filter from Amazon (I forget if it was Mann or Mahle.) Just not worth potential aggravation and cost on such a complex and expensive to service vehicle.

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2003 X5 Sport w/Premium Package M54 3.0L 6cyl