These valves service differently than most anything else, because the entire actuator assembly can be removed and replaced, by any number of different makes and models of actuators. The actuator itself might be repairable, but the economics generally favor complete actuator replacement.
In any event, you must completely remove the actuator from the valve, before you can take it apart for repair. That will involve removing the cover for the vacuum breaker, at which point you might want to renew the components of the vacuum breaker.
Look here for the various service kits.