Engaging park is a steel "pawl" with teeth that is moved via an electric motor. The teeth on the pawl arm engage into the teeth of the gear in the RDM on the output shaft. Its really the same as a normal transmission of a gas engine car but that is connected to a cable and shifter. But cars such as mercedes use the same theory of electric motor to engage park in the transmission. It doesn't really wear out, however when the rdm has an old style clip that holds the output shaft in, the park pawl can wear into the rdm case and cause noise but it has nothing to do with using park.