As far as I know there have been different master cylinders for rear brake having different bore diameters. I suggest to take a pic of it and paste it here, and then let someone to tell who knows.
The parts manual says "PS 12 N" for RGS and "PS 12" for SFC. I don't know does this mean 12mm's.
Many bikes has a changed different master cylinder because they are known not to have touch and too less brake power compared to force it needs. My rear brake has no touch and trying to figure out what kind of master cylinder is better. If someone knows what kind of master cylinder is better and where to buy it, please let me know.
