yes they do - side is for engine air intake wing top is for heater
if both sides of the engine, in fact if most of the engine bay is covered in oil, then this is certainly caused by (as per reds post) crankcase pressurisation - i've had this where on a longish high speed trip you'll notice a smell of oil, opening the bonnet will reveal that the oil filler cap has been blown off and oil has been blown ALL over the bay
sometimes the oil warning light will come on before you notice the smell as oil will be being lost very quickly
