tube between the air filter and turbo, or tube between the turbo and intake manifold??? Start posting pictures. If there's oil in the tube before the turbo (suction side), is there a PCV valve or some other form of crank case ventilation connected to the inlet piping??? If the oil is in the tube between the turbo and engine (boosted side) I'm guessing the turbo oil seal has failed. Does the turbo spin freely with no side to side play??? If you post pictures, perhaps someone with the exact same engine can help.
Is the machine inside where it's warm or are you working on it outside in the cold???. If it's outside, I'm still worried that the air filter could be full of snow. Even with a new filter, under the right conditions, the intake could plug up with snow in a very short time