[68RT]

If you have breathers, it is not a standard arrangement after 1972. Normally (after 1972) they came with a fill cap, hose going to the air cleaner and a pcv valve to the intake area. Breather should have a slight vacuum while running but will vent fumes if the engine is shut down. Breathers on both covers will allow too much air in and will cause venting. If a breather is used, then breather should be on the side opposite the PCV valve causing a cross flow within the engine. Then the fumes will be directed to the valve.