C1391 - Brake Actuator and Brake Accumulator

For those of you that had the C1391 or brake booster failure, did you go ahead and replace both the brake actuator and the brake accumulator? I know Toyota replaces both, but being out of pocket and the parts being ~$600each, being able to determine which needs to be replaced would be ideal. I have seen a flow chart that states the brake accumulator rarely goes bad and most of the issues has to do with the brake actuator. Anyone have any testing procedures they went through?