I’m not sure if this was mentioned before (used search and nothing came up), the m56 engine from a sulev e46 has a valve cover that will fit the m54/m52tu engines and the valve cover is aluminium with an inbuilt ccv. Thereby eliminating the need for the stupid ccv system under the intake manifold.
The only issue is that the VC is only available in the US (available from eBay for about ~$250) and some modification is required; ignition coils change to the push in ones, (IIRC 2001 - 2003 X5 models have the bolt in ignition coils) this requires a change to the push in coil harness.
And the ccv diaphragm + cap is somewhat difficult to find. There is a huge thread on another forum where someone made an aluminium cap which works fantastic.
Also, the dipstick tube needs to be capped off and the plumbing for the vacuum lines from the intake manifold to the VC needs to be changed.
All easy work though.
It’s mostly a straight swap and the gain is amazing. I’ve been running my m54b25 with the m56 valve cover for over a year now with no issues or headaches.
Here is a photo of it;
