Just my 2p, but with something like this you may as well just buy it new from BMW.
https://www.ebay.co.uk/itm/334186758085?hash=item4dcf153fc5:g:HfcAAOSwlTZhbga3 - it's £90, but with any second hand one, you will still have the issue of rusty fixings and heat+vibration to weaken the mounting points.