HI,

Could be the turbo seals, but check the engine breather system is clear,
as back pressure will cause oil drain problems back to the sump,
and oil will pass the turbo seal on the turbine side and out the exhaust
if bad you will see a lot of oil residude in the exhaust ,
check also the air filter is good not blacked, and last take a breather pipe
off the rocker cover and feel if high crancase pressure from worn comp
ring's.

DAVE R.