AT the end on the day id say its best to breath from the rocker aswell and let the hole system breath to atmosphere aswell via a vented catch tank!. Hot oil produces condensation so it needs to vent to atmosphere if u take a truck engine apart and thats an engine that runs 6 days a week for 8 hours a day!. If serviced are as clean as a new engine inside with over 800,000kms on the clock!. Id put this down to the breather systems being so affective and always venting to atmosphere letting all the shit and condensation escape from the engine!. Well apart from this new euro 5 ballshit were trucks have egr putting all the shit back into the engine lol.When i did my exhaust manifold gaskets not so long ago i took my catch tank off for room and when i turned it upside down to empty it u should have seen the shit that came out of it if id had a closed breather system then all that dirty oil condensation water would still be inside my engine!