The second dealer is a muppet.
http://www.realoem.com/bmw/showparts...59&hg=65&fg=45
02 Replace DVD player 1 09/2008 65839241764
That is the part you need. Get them to quote on that part.
You may need to code it, not sure if the drive comes unlocked or not, but easy enough to fit yourself.
I am surprised it is now £80 though, it was £450 a while back, but then the CCC unit was £1800 and now you say it is £675, so maybe it is cheap and maybe they have had a load made as they know drives are not everlasting.
See how much a new one is and let me know. You can have this one cheaper if it is of interest. It came out of a car only a few months old so like new.