dont worry, i am sure you oil vapour is entering up stream from the turbo, but when it cools and forms liquid again, it drops down the pipe to the low point which is the turbo.
all diesel have a certain amount of blowby, but cool running ones on multigrade (there i go again about this) do tend to "breath".
you may find that at oil change time, no matter what the oil used, it is better for a day or two, also oil vapour out of oil filler cap when engine is cold will be zero or very little compared to at normal tempreture.
what sort of oil are you using? good brand or poor brand?
Synthetic or Mineral?
Synthetic multigrade is better at staying "non sheared" but is designed for new engines with no wear and smaller tollerances than engine of yesteryear.
try a straight oil next time, sae30, see how you get on in winter, remeber when we used to change oil grade for winter??
