Hi, yes, I think you are reffering to the PCV valve, No.2:
RealOEM.com BMW E38 740i Intake manifold system
This was replaced about 2 years ago, so not a likely candidate I would have thought. Also, I think you would have got smoke and a wheezing noise if that had gone.
I have put in 8 new coils and spark plugs and 2 aftercat O2 sensors.
I did the repair myself and the timing was 'by the book'.
If you are asking about the price of parts:
2 VANOS units = £250 each.
2 check valves = £10 each.
Valve & upper timing chain gaskets = £50
Timing tools = £300.
Expensive?.............yes!
But worth it just to get shut of that embarrassing noise.
Still no fault codes!
Anymore ideas?
Thanks.