When changing the engine oil filter in a 2009 VW Passat, pay attention to the oil filter seal.
After removing the oil filter hosing, remove the old seal and clean the housing seal groove. Lightly oil the new seal and install the seal with its half-moon tab pointing upward in the canister, toward the block.
Note that this seal may accidentally be installed inside-out, which must be avoided. The proper position has the convex side of the seal facing outward, with the vertical slot facing inside. After properly installing the new cartridge into the plastic housing, torque the assembly to 25 Nm.