I would be very surprised if a valve stem seals were leaking enough under vacuum to show visible smoke, but not leaking while the engine is off. Did you try pouring oil into the return passage and watching flow down? That's a hard place to clean.
This I some basics on valve seals:
Automotive Valve Seals: Symptoms Smoke at Startup
This is great post on the CCV system in the n62. Specifically post 18 has some more tests.
http://www.bimmerforums.com/forum/sh...8#post25763768