No real help other than to say that my 4yr old car (full BMW service history, no warranty extended or otherwise) has just had the sunroof cassette (ie whole sunroof) replaced for a cost to me of ?620. BMW did 80% goodwill on the part and they gave me a fixed quote for the labour.

Thanks Dave thats useful to know. Do you think the super deal you got was because you get servicing done with that dealer? If the worst comes to the worst I may have to see what my local dealer can do on this although they don't currently know me or the car so perhaps would be less open to this kind of arrangment

If anyone can help me to diagnose the fault without having to take it into the dealer I'd be greatful of the help