I used the top, slotted opening in the engine to add oil when I did my oil change the other day. At the BMW dealer, Mike noticed that there was some seeping from the cap. He suggested I take an emery cloth and clean up where the O ring goes.
I got home and removed the cap and the O ring, and noticed the inside of the cap and some of the threads had black paint on them. I used the wire wheel and removed the paint on the threads and the inside of the cap. I then cleaned that up with a little fine sandpaper, reinstalled the O ring and went for a ride.
No seeping noted.
