Help me please.

I have a Jap import Daihatsu that has recently had the engine replaced. The car uses a two coil packs and a wasted spark system for the other two cylinders. On each of the coil packs is a small pipe that is an air vent from the spark plug cylinder tube and the other two leads have similar air holes. After removing the coil pack cover(pit of plastic that goes the length of the engine) I smelt an oil/fuel smell when the engine is running. I have traced this leak to one of the coil packs pumping pumping air out of it. It smells exactly the same if I take the oil cap off. I have checked the plugs and all are correctly tightened and there is no visible sign of oil. I assume this vent allows the head to breath in some respect but does anyone know why they are there and if this is a common thing on engines or is something wrong ?

Thanks for any info.

David