Worn valve should push harder on lifter but still could be lifter related. If the lifter has a favored position it may not compress quite enough.

I would try both thicker and thinner oil.

On the N52 BMW has a procedure to reduce the tick that basically is keep the revs high under power for 30 minute (eg use m/s to hold to 1 gear lower). I would try the same procedure on both higher and lower viscosity oil.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)