At the same time, I managed to free off the last of three bolts holding the hydraulic unit together. The front section has seals visible, one to seal the two parts together and one just inside the gold coloured tube. The booster has two o-rings. There is a bolt on each half of the unit. Perhaps someone knows if removing these allows access to the internals somehow. Both of these on the refurbished one have been removed, cleaned and plated. The master solenoid on the front looks to be held in with a clip so may also be removable.