Ford Transit 2.2 TDCI 100 PS presses a lot of oil through the valve cover seal.

Hello forum members, have bought a transit with 220 Tkm from a dealer. When buying, the dealer told me that the valve cover seal was renewed because it was leaking and otherwise everything would be fine. Vehicle runs very well. Idle running constantly at 850 revolutions and top speed is at 150 to 160 on the straight. After 3000 km again pushes a lot of oil out of the valve cover seal. What’s the problem? Does anyone have experience with it? Greetings Bernado