The oil is coming from the intake track, check the joint close by the area you are concerned. You will find it oozzing there. Next question is why is there oil in the intake track? It is getting sucked into the turbo form the PCV valve. Next question why is it there? Check your oil level, it probably past full. How did that happen, during DPF regen the engine is injecting fuel during the exhaust stroke and it is blowing by the rings, diluting the engine oil, thus making the oil go up. What is the fix? Only fill the engine with 4 L of oil and not 4.5 L. That will show up about mid dipstick when you check it. And allows the oil to increase in the crankcase plus eliminates whipped up oil vapors from being there in the first place occuring because the engine oil is too high. The next problem is that the bottom of the intercooler is full of oil, need to remove it and drain it out. That is a little bit of a job. Gee how do I know this, Yeah it happened to me too.