Thank you, aerobod for your advice. I believe retainer strip (white plstic plate on the 2nd photo) is properly attached to the body side (body side has holes and retainer is attached with the projection part in the body side hole to slide in click.) Do you think some parts are missing to click in, such as No. 8 expanding nut and/or No.7 hex head screw in this diagram:
(
https://www.realoem.com/bmw/enUS/sho...20#51778056817)
Any advice, please.