A slightly better horizontally opposed engine will burn a little oil, which is a structural issue. Plus, 20-weight oil tends to evaporate at high temperatures. However, it's generally not very serious. If you add 4.7 liters and there are still 4.2 liters left at the time of maintenance, which is above the lower limit of the oil dipstick, then it's considered normal oil consumption and there's no need to worry.
