My experience was totally different. Intake had oil, pipes had oil, replaced all seals imaginable and prayed- valve cover seals and every other seal while at it ... twice! Still smoked on extended idle 10-15 minutes when engine is hot. I tell you I really tried to avoid doing the valve stem seals. Nothing worked. When I finally decided to change the valve stem seals, they were in fact brittle and most would barely seal the stem, the gaps between the seal and the stem visible on many of them. Smoking and foul exhaust smell stopped after the valve stem seals replacement.

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.