I don't think we ever changed the CCV, and based on what I read, that might be the likely culprit.

Generally no smoke or smell. We did have smoke after replacing the plugs, but it burnt off quickly and we concluded that was the oil that dripped into the cylinders when we replaced the plugs.

Replacing the CCV doesn't look like a DIY job for me. I have read some DIY, and looked at some videos on youtube. Unless it's much easier to do on a 3.0 E53 than the other models I found, I will either take it to an indy or have my mobile mechanic do it. What have others paid for CCV replacement on E53 3.0?