im in the middle of doing a TB job and when i took off the turbo piping there was "not a lot but enough to notice" residue of oil what could be the cause?

 

is it in the pre turbo pipes? if so than you need to fit a catch can... if its in the post turbo pipes than it could also be the seals in your turbo leaking but its most likely just the poor PCV system and a catch can will solve that.