1. In order for anyone to help you will have to let us know what motor you have? We know its an X5, we'll assume thats why you're here, and not asking the question on a GT-R forum.

2. This is where you will find everything you need for your motor: RealOEM.com Online BMW Parts Catalog

3.The following finding is based on my '01 4.4.... For me it would be #4, part no. 66216902182. But this will be different for you as it states this only goes to 02/2002 RealOEM.com * BMW E53 X5 4.4i Park Distance Control (PDC)

4. As for the ebay item(s) check on realoem and cross reference the part no's by asking the seller if they are compatible.

5. If you use the 'Search this forum' facility in the 'X5 Forum' which is located at the top of the thread list on the RHS, and (as a suggestion) type in 'front PDC', you will find a plethora of threads/posts on the subject.

Good luck, welcome to the forum, and let us know how you get on.