Here is a New Old Stock Genuine ATE Rear Wheel Cylinder Repair Kit (for one side) for 

BMW

2002 Turbo 1973-75

2800 CS 1970-72

E12 518 6/1974-5/1981

E12 520 6/1972-1/1979

E12 520/6 8/1977-6/1981

E12 520i 10/1972-7/1979 models.