Originally Posted by GraphiteGhost

If not, I had a major clue (in my opinion) yesterday! The Mobil1 filter I got with the Advance Auto oil/filter (first Mobil1 filter install on my XF) sale had a note in the bag with the 5 rings. The note says in part "1. Remove drain plug from housing cap if present and allow oil to drain from cap. Remove housing cap, old gaskets/o-rings and filter element. Discard the used filter element and gaskets/o-rings in the proper manner." then step 4 last sentence "Reinstall the housing cap drain plug if present to the proper installation torque." with a few more steps and instructions typical to an XF oil change. So, I offer that 'housing cap' may be on MB's or other vehicles with that particular setup. Finally, the filter has a rubber section (center top/bottom) that locks extremely easily into both the filter and shaft of the cap It slipped on so easily with a light coating of new oil and 'popped' securely in exactly the right place. The top-most 'O'ring (in my cap) was placed in the second groove ABOVE the ring with the small slot at one position on the radius of the ring. I know many have put that ring in the wrong place and had a huge leak/problem/mess. If your cap has this slot in the correct ring near the top, you sould put the 'O' ring right above that ring. Also, I converted the '25 N-M' on that filter cap to @ 221 in/lb which is the proper torque spec for my 2008