S54 rocker arms need to be replaced for every new cam as well as being a normal wear item. Cams and rockers wear together. The rocker is shaped like a finger with a pad on the end. The pad wears along with the cam lobe. Once the pad wears down valve adjustments are impossible (there isn't a shim big enough to fit with a worn rocker). Schrick manufacturers these rocker arms to be more consistent quality and material than the factory BMW arms. They also have a DLC and graphite coating by Schrick in Germany. DLC stands for "Diamond-Like Coating" and has very low wear rates. The graphite additive reduces friction which lowers temperatures and keeps the oil from thinning in a critical area.
Rocker arm wear is not a very big concern for the S54 but only regular valve adjustments will indicate how much they have worn. And new rockers are required with new camshafts. Schrick camshafts must use
Schrick rocker arms (not stock).
These are sold per rocker.
E46 (99-05) > M3
E36/7 / E36/8 Z3 (96-02) > Z3 M - S54
E85 / E86 Z4 (03-08) > Z4 M