BMW Repair: X5 Using oil but no leaks, air leaks, pcv system

Question
I have a 2001 BMW X5 3.0L which is using oil yet has no obvious leaks nor pooling under vehicle. I am having to add about 6 quarts approximately every 4,000 miles.Could this be caused by a non-working PCV system? If so, how difficult/expensive would it be to replace? Any other ideas?

Answer
I think you are on the right track.!

Check for air leaks ANYWHERE on the engine.
The breather hose to the rocker cover only has a fine mesh  filter seperating the oil fumes and the intake system. An air leak, increases the flow past this filter where as it cant seperate liquid from vapor quick enough and thus you burn it!

Other than that, the engine is worn out, but we both know thats not common on a BMW.