Classic Mini Brake Master Cylinder Repair Kit For GMC171/2 Post 1985 

All the single line .70" bore brake master cylinders as used on the Mini and NOT the same. They make look and function the same but ever since about 1977 the internal working have been changed from a 'cup and ring' seal system to '2 rings'. Remember that in all probability if you have replaced a master since 1977, your system might be the 2 ring type rather than the original. 

Part number for reference: GRK1006 (BAU1247).