brake actuator replacement plans?

I think I need to replace the brake actuator on my 2005 Prius with 250k miles and new hv bat, but want to run the symptoms past you experts to see if there is a another option I should pursue.

I got these codes and lights:

c1241 low or high battery voltage
c1256 ACCumulator low pressure
c1391 Abnormal leak of AC pressure

Techstream shows the aux battery voltage was 14.1 volts

BRAKE red, ((!)) yellow, ABS yellow

I notice in the morning when I start it and put it in reverse with my foot on the brake, the car rolls backwards for a second as the brake pedal falls quickly for a few inches, then the pedal provides resistance and the car stops. I had this problem for about a month, then the trouble lights showed up while driving on the expressway yesterday.

I never changed the brake fluid, and the brake fluid tank is full.

After reading forum posts last night I concluded the brake actuator is bad and that I missed the extended warranty for this issue and never received a letter on the topic.

1. Is there any chance flushing and bleeding the brake fluid will correct the brake actuator problem?
2. What part number actuator should I look for? I will buy a used one and install myself. I read newer actuators have a design update for more reliable performance so what is the pn for that version? My vin is jtdkb20ux53056101
3. Should I plan on changing anything else in the area while I have it opened up to change the brake actuator?
4. Why do I have the c1241 bad bat voltage when I have 14.1v? What is the acceptable voltage range?
5. Is there any other chance at a warranty replacement for my old car? I seem to have missed last years opportunity.

Thanks in advance for your great advice! I want to keep this car running as long as possible so I do not have to take on a new car payment.

Thanks,

Doug