Service kits are built for the 7 variations of all OA21 Units and all ONIX AUDIO units that were produced between 1984 and 1992. These are provided from stock parts, that we have sourced so as to keep the integrity of the original units . They are the most likley parts that will degrade with age or by service life and use . It will require a good engineer to fit the parts we provide and all parts are tested before despatch . Parts are not about specification . These are parts that are listened to and are replacements for original parts .