I've done it on the E46M. It's just getting to it that is a pain. I used a large flathead bit socket and an extension onto a ratchet. It came right off. I recommend just swapping out the o-ring.
http://i1212.photobucket.com/albums/...y/IMG_0277.jpg
http://m3forum.net/m3forum/showthread.php?t=369406
Everyone should do this when swapping out headers because access without the headers makes this a 5 min job max.