Hi All, thanks firstly for all the info, I have a w205 with the exact issue relating to the roof chords, just had diagnostic completed and a quote from MB for £10,300 to replace the roof unit completely.
Thank you. I think I might go to an independent merc specialist near me. Merc dealer wants me to pay for diagnostics just to have a look, although we already know the problem.
The independent merc specialists is charging me more than Tony in Coventry, but unfortunately it is a bit of a trek from Norfolk.