BRAKE MASTER CYLINDER REPAIR KIT FITS GMC171/2 POST 85

All the single line 70" bore brake master cylinders as used on the Mini are NOT the same.

They may 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 '77, your system might be the 2 ring type rather than the original.