Finally, there is a source to rebuild Servo Brakes on 2005-06 RT's and GS's:
http://www.modulemaster.com/en/index.php
http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=779028#Post779028
http://www.modulemaster.com/en/index.php
http://bmwsporttouring.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=779028#Post779028