If the rubber diaphram in the CCV is torn, there will not be any external leaks, but the engine will actually suck oil from the dipstick tube (and combust it... your cats will catch it and because it's not a huge amount all at once, you won't see smoke out your tailpipe until it gets REALLY bad - but unchecked it's a good way to ruin a cat and those are BIG MONEY).

If you have no external leaks, I can almost garauntee you that your oil consumption problem is separator related.

The V8's are known to eat more oil (valve seals, etc), but the 3.0's shouldn't be eating any more than 3-4 quarts between 15,000 mile oil change intervals.

I'm an SA, and have had several M54 cars. When well maintained, I average 1-2 quarts between 15k intervals.