Originally Posted by David.X5

To Semcoinc- yes that is the part. Yes, works for every key. It attaches to the back of the keyed part of the cylinder. Find some instructions on removing the steering column trim (pretty easy) then disconnect the plug and 1-2 more screws and your done. It's so cheap and easy I wouldn't wait very long if you have that no-start problem. Could be something more serious, but given the age of our E53s, these sorts of parts will need replacing soon anyway.

Check the BMW part sources (ECS tuning, Fairfax BMW parts, etc) That's about the same price I remember paying for a genuine part.