What cause to have oil leak at the inlet to turbo?

Hello, Like everyone else with this engine, you will eventually be told that your rear main seal is leaking, though, light everyone else with this engine, it will not stop the oil seepage. Turbocharger systems pull and push air through the engine, not just for combustion, but for ventilation of blow-by in the crankcase and heat in the cylinder head. That being said, there is always a fine mist of oil floating through the air in the engine, and that builds up in the charge piping, intake manifold, turbo housing, intercooler, and even the air inlet tubes. It is par for the course. These, and VW/Audi seem to have more issues than most, but unless you start dripping oil, addressing the problem every time seepage is noted would become very expensive quickly. The reason I say to address the issue if oil drips begin to occur, is the central housing rotational assembly (CHRA) oil seal can fail, and that can destroy the turbo, and anything downwind (engine). Many owners have installed catch cans for oil to prevent buildup, but, like I said, it is par for the course, and unless it drips it really hurts nothing. Consider having the intake tube and charge piping removed to see if there is excessive oil drainage form the turbocharger oil seal.