I come from the E39 (1998 528i) world and the cap is ATE type for E39.
I wrote a DIY for E39 brake bleeding using ATE Volvo Cap so I can bleed the brake using the air compressor:
DIY: 1-man Hydraulic Bleeding Kit for those with Air Compressor! - Bimmerfest - BMW Forums
It should be the same as E53, I will verify later when I have time.
Edit: E53 or E39, same cap:
http://www.xoutpost.com/images/artic...rakebleed.html