Is it actually my ABS Brake Actuator Assembly? ABS, VSC, (!), BRAKE lights

I have a 2005 Gen II Prius with 136K on it. I bought it used over a month ago. The VSC, ABS and (!) light along with the red BRAKE light started coming on a little over a week ago, while on there is a continuous rattling like the regenerative stuff is going on. Hills and bumps seem to be a partial source, but do not always trigger it, and are not always present. The lights seem to go away when I take sweeping corners, but can return almost immediately. Normally car has been running for 20-40 minutes before the lights come on. When the lights have come on when I've been on the freeway, a screeching warning alert comes on after a couple miles and stays on for a couple miles before all the lights and the screeching goes away.

The codes that Toyota pulled after the screeching happened the first time were: C2318, C1242, C1252, C1253, C1355, C1377

They replaced the 12V battery and then pulled the code C1253 after I got on the freeway home and the lights came back.

They recommend I have a new ABS brake actuator assembly for $2800 installed. The lights coming on are noted in the service history of the car in July and August before the previous owner sold the car.

On Friday, I pulled the car tight all the way around a traffic circle to turn around. The lights went off and have stayed off since, with about 100 miles of driving since then.

If this is actually the ABS actuator assembly failing, would it go away for long periods of time? Could it be something else? If I do need the actuator replaced, is getting a used part a bad idea?

Thank you to anyone who can help! Let me know if you need more details.

 

I will ask the dealer, thanks.

Also, I checked the service history again and it turns out that an ABS light was first reported in August 2012 and then again in July 2013, so the times were farther apart. If that makes any difference.

 

The dealer tested the relays. The lights coming on and the shrieking sound are happening more often now. Is there a simple way to turn off the noise until I've gotten this into the shop? I guess I'll just have to bite the bullet and have the ABS brake actuator assembly replaced.

 

I'm in Seattle, WA.