It is valve stem seals, common issue on the N62/TU, done lots. If the smoke is very recent then valve seal replacement will correct this issue. Valve seals only replacement is 2.5K+.
If the issue has been on going then you may need to pull the heads and replace the valve guides and clean out the secondary air ports on the head. Valve guide replacement is 6K+.
There have been a small amount of issues with the vent valves on the valve cover(s). They are cheap and easy to inspect and replace has they pop off of 4 clips on the valve cover.