I'm still confused on rocker cover breather hose at the rear and the PCV at the front. What stops the oil and that going out the breather at the rear of the rocker cover instead of working it's what through the PCV?
Also, if you removed the rear breather hose and replaced it with a breather filter thingo would that cause a drop in oil pressure?

there should be a baffle under it.

sort of like an L shaped piece of metal.

Becasue the PCV "sucks" the exhaust gases/whatever from the crankcase into the manifold. That's the reason it has a check valve - so the gasses can only go one way.

The breather hose allows air to enter the crankcase to fill the vacuum being created by PCV. In order for oil/gasses to travel back through the breather hose, the PCV valve must fail and and allow air to travel the "wrong way" through it....

Nothing to be gained from putting a breather filter in there. Oil pressure would not be affected (you can run the car with the oil filler cap off if you wish!) but it may introduce a vac leak...

Earlier models with early injection systems ran VERY ragged if you loosned the oil filler cap OR the dilstick wasn't pushed in properly to seal

Thats because of the ' breather hose' from the rocker cover to the throttle body. Air entering thru this hose is not recognised by the ECU as it is after the air flow meter.