I have had to add 2 liters of oil in 10,000 miles, is this normal? on 2004 Mercedes-Benz E500

There has been a leak around the valve cover. How can the problem be corrected?

Asked by for the 2004 Mercedes-Benz E500
on alot of car if it does leak or burn oil you will need oil
there is gasket that needs to be changed under the valve color