The more I think about it the less I think it’s the turbos, as you say I’d be seeing smoke when at temp rather on cold start.
My head was fully rebuilt when I had the head gasket replaced only 6 months ago so I also no its not valve seals etc, cars now 79k. All work was done at Darren Woods so I have no reason to suspect poor workmanship.
Thinking about it, there must have been something that caused the head gasket to go first place and the obvious is excessive crankcase pressure possibly caused a blocked faulty PCV system?
Only thing that puzzles me is where the feck does ¼ litre of oil go in 400 miles without any smells / leaks? Does this fit in with a PCV issue?