Oil leaks from the cam (or rather, rocker shaft) cover more or less came as standard with many 1950s/1960s cars after a few years. With the engine running and the oil filler cap off, any excessive fumes should be visible or felt if you put a hand over the filler hole.

They haven't been vented to air for many years. Crankcase breathers have vented into the inlet manifold since the sixties at least, usually via a vacuum operated diaphragm valve sat on top of the manifold.

The EGR valve is just a fancy way of precisely controlling when and how much is recirculated and also allowing controlled venting into the inlet tract upstream of the blower on forced induction engines.

The crankcase breather runs into the pipe that is connected to the air recirculating system which includes in its path the EGR.The air from the crankcase breather is either recirculated into the engine or burnt in the DPF have a look at your own system and learn befor you critise.

No-one's yet managed to answer the OP's question.

If it were mine, I'd find a pipe from the rocker/cam cover to the inlet manifold. I'd disconnect it at the cover end and with the engine running see if it's blowing any fumes. I'd ensure the hole in the cover's clear and also the pipe to the manifold. I'd also ensure all the fixings holding the cover down were tight.

Modern diesels do have their own version of a PCV valve used in throttled engines; it's called the Crankcase Pressure Regulator. It operates on the tiny pressure drop between the air filter and the compressor inlet. It's possible that the CPR has become clogged and isn't opening, allowing pressure to build in the crankcase. It might be worth taking the CPR off and carefully cleaning it. 'Carefully' is the operative word, the diaphragm is easily damaged by caustic materials or careless handling.

Just follow the breather hose back from where it joins the air intake until you come to a junction. The valve will be in the housing.