A crack you can see, warp you can tell and leak point you can find. I would remove the valve cover and verify the cause of the problem.

My guess is if you use an OE gasket, install as recommended by BMW and torque down the cover in the proper sequence it won't leak. OE gasket is cheap compared to tearing it down again.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas