I finally decided to pass the speedo to this guy:
http://www.guagerepairs.com/
Not cheap at £160 but better than the prices advertised for a recon speedo at some independants which can be as much as £240
I only wanted the glass professionally repaired really but Peter will only do a full clean up service and I suppose if the outside of my speedo was such a mess there were probably bits inside that needed cleaning and repairing as well. That said, for £160 I would have like to have seen a new rubber boot fitted on the reset button. Peter informed me it would be a 6 week wait and it turned into 8, he also mixed up two BMW instruments and sent mine to another customer and I recieved his, it was sorted pretty quickly though and mistakes happen.
Here is the renovated speedo, It looks a million dolllars compared to when I sent it off and I have the satisfaction of refitting the M/Cs original part rather than a replacement.