My 2.0 8V turbo engine slightly smoking blue (very little, but quite noticable) under certain conditions - only when using the gears to slow the car down or when revving the engine above 4000 rpm. The engine has been fully rebuild about 6000km ago, and the head has been fully rebuild 500km ago (including all new guides, seals etc). There are no visible external leaks. THe engine does not smoke on idle (cold or hot), under boost or while cruising. The compression is 118-120-121-120 (1 to 4)... any ideas??? And I am using Mobil1 fully synthetic 10W30 oil.