I recently acquired this 2011 E350 Bluetec and its leaking oil everywhere. I've isolated it to the oil filter housing as that is the place I see the oil pooling on the serpentine belt and the gaskets appear to be leaking as evidenced by the oil all over that area. I've been trying to get past the cover over the serpentine belt that has two bolts and what looks like a catch near the bottom. Seems like you would just lift up on it but it won't budge and I don't want to break it. This is the cover between the fan and the pulleys. It almost looks like you have to remove the entire front of the car to replace the serpentine belt, but that would be ridiculous. Workshop manual procedure would be amazing if anyone has access to them.

Once the two bolts you see loosened in the image have been removed the cover will move from side to side and the rubber surrounding the bottom insert seems less that cooperative to releasing.

 

It released. Pushed up from the bottom with a wood handled hammer by focusing the force on the nub sticking out of the rubber grommet. Also applied oil to the top of the nub to aid in removing all potential friction. Now, it appears that in the bluetec, the fan needs to come out because the turbo sound dampener is sitting in front of the serpentine belt. Best I can tell, the serpentine belt needs to come off to remove the oil filter housing. Removing the fan and the turbo sound dampener makes room for that to be possible.