Genuine AP Lockheed replacement master cylinder for all Minis 1980 to 1988, apart from some Canadian and export models until 1982ish. This master cylinder is identified by a yellow ID band. Usually these master cylinders are very reliable, however, when they go bad it is often better to replace rather than rebuild. The fittings are metric, M10 on top and M12 for bottom. 
 
Pre 1985 Minis will require a standard to metric conversion kit (WC-BAU5654MS for RHD, WC-BAU5655MS for LHD) for fitment.
 
These master cylinders can also be retrofitted to earlier dual line cars provided the lines are swapped and connected properly (Front brakes on top, rear on bottom).