2001 C70 2.4 arrived with a blown head gasket and a clogged up cooling system from a bottle of "head gasket sealer." Head planed and new valve seals installed by machine shop. The sealant all through the engine reminded me of the expanding foam for insulation. I scraped it out of every orifice that I could.
Now, at random times, but particularly as the temperature is going up, a bunch of burnt oil smelling blue smoke will waft up (typically while idling for long periods of time or on re-start of hot engine). I have not noticed it ever on a cold start. PCV system seems to check out fine.
Theory: coolant line to turbo clogged, getting things in turbo pretty hot and seals failed. Possibility? If so, could this be reversible by getting the lines unclogged and getting it to run at normal temps. If not, what type of job is replacing turbo or is there a possibility of just changing the seals in the turbo?

 

check the 850 board - quite a few postings on rebuilding turbos - some with pics. If your oil lines are clogged you should also check out the vids on "Seafoam" treatments or read up on using transmission fluid in the engine to try to clean out any sludge. Look at the intake to see if the PCV has pushed up any oil that way as well. Did you try putting a pressure gauge on the oil to see if its normal or possibly too high?