Started having high oil consumption..needing a quart every 3k m...before it was about 1-2 quarts in 15k m change interval. I'm not seeing any leaks and can't detect any blue smoke from the exhaust. Started happening suddenly, already used 4 quarts with 3k m still left before oil change.

Any ideas what it could be? Something with crankcase oil separator maybe?

 

you might not notice a leak if its dripping down onto the plastic under carriage panels

 

Inspected everything underneath and not seeing anything leaks or wet spots.

Ordered new spark plugs, will see If I can spot anything unusual when I remove the old ones. Otherwise the engine runs well.

 

You will likely need new valve seals. Search you tube for a video on how to diagnose bad valve seals on N62 engine. Also check out the All German Auto website. They sell a tool that allows you to changes that without excessive engine disassembly.

If this is your problem and you take it to the dealer it will cost thousands of dollars to fix.