Select as Best AnswerUndo Best Answer
Try using vagcat onlinehttp://www.vagcat.com/epc/cat/vw/LU/Select your year and browse away through the blown up diagrams.
Oh and it does require a quick free registration but you will find the part number on this site!
You could take your Lupo to a garage and ask for a written quote for replacing the part and fixing the door - the quote should detail the part or parts required.You could photograph the part, and email the photo to VW. If you are in the UK, click here for contact details.