Not sure I agree? Crankcase oil fumes are normally fed into the system after the turbo. That said this does raise a question of how the engine block/sump is not under positive pressure.
I think (when I get a chance) I'll look at Croma eLearn (or other diesel turbo system) is plumed.
Regardless of turbo, no turbo then the pictures provided of that intake manifold show nothing but carbon crap build up. You do not get this with any carb or petrol injected vehicle even with EGR.
Diesel engines create soot. Even modern ones with DPF when run/booted "out of optimum range" create soot. That is why I've always maintained the diesel engines are NOT suitable for *dynamic* operation. Diesel engines are best suited, tuneable and clean when under designed constant load.
And electric car with a fixed load diesel generator can be made to be very clean burn.
Soot + oil = crud as per the pictures presented.
There is nothing wrong as such with a diesel engine when run in accordance/sympathy which what it is good at. Sadly IMHO motor vehicle as in cars is not IMHO a good use. Long haul trains, road trains, etc. then yes but not urban, semi urban stop/go etc.
If diesel was not dirty then why were DPF filters ever created?
And yes modern petrol vehicles are now having some form of filter introduced.
I fully know and accept that I'm posing a pointed (would not say biased) point of view but IMHO a huge mistake was made several years ago road haulage, agricultural, etc. diesel fuel usage was promoted to personal car usage all possibly based on some value target (eg CO) and not on overall pollution.
Bloody complex fish bowl!