2010 Prius - Leaking accumulator/Check Hybrid System P0AA6

Greetings,
New here...looking for some help with the problems in subject line. Any advice, directions etc are appreciated. Not very familiar with hybrids, but trying to learn.

2010 Prius w/ 235k miles

Problems/conditions:

-The brake booster pump (correct term?) runs/cycles every couple seconds until car is turned off. I can hear a noise in the area of the brake booster when car is off, and the car has shown before the trouble code related to the leaking accumulator (but oddly is not showing it now).

-Separately, car constantly shows "Check Hybrid System" and has the P0AA6 code. Upon first startup, I can drive it with no abnormalities for a short distance (1/4 or 1/2 mile) but then something strange happens: the brakes no longer will regen correctly while braking, and the traction battery level indicator begins to drop noticeably. It should be noted that there is no braking trouble prior to this happening, everything is normal until the trouble begins.

I note that once this braking trouble occurs, as I brake or coast, instead of it registering on the regen bar as normal, it indicates on the right side of the regen bar, as though I was using power while braking/coasting. I hope I'm writing this clearly. I'm guessing this is a direct result of the leaking accumulator?

-Traction battery is only several months old (GreenTec auto) and charged; I have a grid charger to keep it full. But the CHS message displayed both before and after the new battery.
-12V battery a month old and charged.
-Getting frustrating.

Questions:

1. Can a leaking/malfunctioning brake system in these cars lead to/cause a HV battery isolation fault, seeing that the regen system is connected to the battery in some way? I wonder if these 2 troubles above are related in cause.
2. I don't have Techstream to read the P0AA6 subcodes; can someone direct me how to get it on a laptop?
3. Are there any known 2010 Prius isolation fault items I could check right away to eliminate anything off the top?
4. Brake accumulator: where to obtain besides Toyota? Any refurb units or any such options out there?

Thanks for any assistance. I've used this forum in the past and am grateful for the previous advice, now would be so glad to get some help on these specific problems. I confess I have not yet fully researched these 2 problems on this site yet. Hoping someone has experienced this before.
Standing by to give more info if needed.
Thanks, Eric