This will allow the crankcase to vent excess pressure without allowing oil to escape. Oil blow-by from the piston rings pressurizes the cam housing during combustion and pushes down on the cam oil seal. If the excess pressure has nowhere to go the cam oil seal may blow out.
Ensure proper crankcase ventilation system and consider installing larger diameter hoses and lines as needed. Install new PCV valve of proper specification or ensure PCV is operational for that particular 3.5 liter Isuzu as some years used manifold vacuum as PCV system.
