A4 oil leak

HI can anyone help?
Just had my a4 2.5 diesel quattro serviced and timing belt changed. 500 miles later oil warning light came on and it had lost 2 litres of oil. Called back the service guys and was told it was rocker cover gaskets. Still leaking and now being told its the cracnk seal and the plaste seal behind. Has anyone else heard of this problem

Thanks