Digging up an old thread here but just wanted to share my experience for others:
New to me 06 4.8is with 77k was producing white smoke after extended idle (~ 5 min or so). Of course I assumed it was the dreaded valve stem seals.
Anyways, after reading this thread I pulled the engine covers and investigated my CCV system. Found that the diaphragm on the right side had a tear and the breather hose on the left side cracked open. The PO (or their mechanic) choose to repair both with Duct tape!
Ordered new hoses and 2 CCV valves for both banks and cleaned inside the housings. Reinstalled everything and my smoke is gone!!! I expect oil consumption to improve (although I need to address small seep at top of upper time chain cover next).
Many thanks for this post! $60 in DIY replacement parts sure beats a valve stem job!!