Might be wrong but in summary (with HB Chris support) most of E9 were having push rod mount and they were typically chromed die casted ZAMAC (mount) / stamped inox (arm).
Some cars with black trims (color dependent?) were having black arms.
For 1975 it looks All models were equipped with black-painted, nut-mounted arms (unification with other models?)
It can be seen on the original brochure for 2.5CS where chrome trims on the fenders are used with black wiper arms (also visible lack of rear bumper over riders).
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