just changed the oil & looked at things while under the car. i noticed the rubber bellows on the turbo is oily. this is the one that goes to the air filter ( cold side ).
do you think the turbo is leaking, or is this oil from the pcv system?

 

Most likely from PCV. That discovery is what started my adventure into valve cleaning and catch cans.

 

Here's something I would like to look into, just because.
Does the compressor wheel get gummed up do to the oil?
When I did a lot of 3208 TA Caterpillar boat engines this was a problem that would cause boost problems. Oil vapor from the breather was directed into the intake of the turbo. Would have to R&I the compressor housing and clean the wheel, housing and plate for center section. These engines did not use synthetic oil.
When I installed my K&N intake pipe I too saw this oil on my SS.
When I sprayed intake valve clean to help clean the valves I sprayed it in from the intake pipe after the MAF sensor.
Did it help? Not sure, but it couldn't hurt.
When weather gets warmer I'm going to clean the intake valves and do away with the internal PCV valve.
I now only have a small air/water separator between valve cover and turbo fitting and am curious to see if this at least slowed down oil on the compressor wheel.

 

OK used Google to see if i could find an answer to synthetic oil on the compressor wheel causing a problem and can't find an answer.
My only answer to this is, there are no reports of this "problem" ever happening. I looked at other GM turbo makes/models that have the same issue as my only source of info.
My car has 50K and boost comes up very quickly, so I'm going to say, no to this question.
But I will say if the intake valves are not cleaned there will be a difference in fuel economy and power. There I can see a problem due to the heat at the back side of the intake valve is much higher than at the front of the turbo causing coking.