Hi Gordon, as you would be aware, the servo unit is made up of two distinctly different components, namely the Master Cylinder and the bellow itself.
As far as the Master is concerned, my brake people will not rebuild them - it's just not worth the effort and time, with no guarantee that the end result would be satisfactory. Better to buy a new unit after-market, if available. Let me know if you want me to do some chasing around for you.
As far as the Bellow is concerned, just get a price from the people in S.A. Those I can get rebuilt for you in Sydney, and whilst I have had only three done over the last few years, two I know of are still working perfectly
satisfactorily in two of the cars. The jobs are about three and five years old.
Regards Styria