One new original Ate brand 20mm bore major brake master cylinder repair kit, part number 0370-0720.  This fits:

Opel GT 1900 1897cc 1968 - 1973

Opel 1900, Manta 1900 and Rallye 1900 1897cc 1970 - 1974

Opel Kadett B 1.0L, 1.1L, 1.2L, 1.5L, 1.7L, & 1.9L 1966 - 1973

Opel Kadett B Rallye 1.9L 1971 - 1973

Opel Kadett C 1973 - 1975

Opel Olympia A 1.1L, 1.5L, 1.7L & 1.9L 1967 - 1970

Opel GT 1100 1968 - 1970

Opel Ascona 1.9L 1970 - 1974

Opel Rekord C 2.2L 1966 - 1968

Opel Rekord D 1.9L & 2.0L 1972 - 1977