I can't find this part, it's the flat rubber piece that goes under the stainless rocker cover in the doorway. Fits under the piece then about an inch sticks out towards the rocker cover. Can't find it here, I think it fits under #15:
http://www.realoem.com/bmw/enUS/showparts?id=3435-USA---E9-BMW-3.0CS&diagId=51_3430
http://www.realoem.com/bmw/enUS/showparts?id=3435-USA---E9-BMW-3.0CS&diagId=51_3430