If you did an oil change or just had one done, it could be the top O-ring on the filter or the large nut at the bottom of the filter housing (#8 in diagram).
Or as Drewbush said the O-rings in between the cooler and filter housing. The two seals in between are #112 184 02 61 & 112 184 03 61 and the seal at the bottom of the housing is 112 184 00 61 (#6 in the diagram). Here are the instructions.
Or as Drewbush said the O-rings in between the cooler and filter housing. The two seals in between are #112 184 02 61 & 112 184 03 61 and the seal at the bottom of the housing is 112 184 00 61 (#6 in the diagram). Here are the instructions.