Roojai

Good mechanic is working on it but a bit stumped for now, will be doing more investigation but thought I would ask for ideas:

Symptoms:
Bluey-white smoke out of exhaust. Smells like burn't oil, mechanic reckons burnt on hot object smell, not through combustion. No smoke when engine is cold. When engine is warm, smoke is emitted a bit on idle, but mostly at about 2000 rpm on a cruise, or slowing. On acceleration no smoke, and above 3000 rpm no smoke. Seems to be when the throttle is only slightly open. When the conditions are right (eg slowing down with throttle very slightly open and at about 2000rpm) there is LOTS of smoke, trail behind car!

Ruled out:
Oil level is fine! (Recently changed to castrol RS10-60 though).
No oil leaking from turbo on inlet side.
Piston rings: no smoke at high rpm/high boost

Currently checking for burnt oil in exhaust/downpipe to rule out turbo problems.

Any ideas?