The valve now cost $85 on Amazon in 2024 but there is a kit you can get which would cut the price about in half. I think you probably could have just cleaned it out. That’s what I usually do. These things aren’t cheap. i’ve had the same valve now for 31 years.👨‍🔧

The valve assembly (see 2:35 in the video) can be disassembled: using a vise, grab the brass disc at the very bottom (he's holding it in his left hand). Then use a screwdriver on the other end of shaft to unscrew it. You will find a small O-ring on the shaft and a standard faucet washer as the working part of the valve (Pry it out).

You lost the sound for most of this, but it's clear what the problem was. It seems that these could be refurbed easily enough after a cleaning. (I'm here because mine isn't working - except for a dribble. Probably looks like this one inside, full of guck.) The Watts website page on one of these recommends cleaning it twice per year, as maintenance.

WOW! That's messy inside and I highly suspect ours will be the same or worse. We've had issues in our area where the city has done work under the street and when they turn the water back on, there's a lot of brown sediment that needs to be flushed. So I suspect that is the problem. I'm not sure if cleaning that and the preventer is going to be a long-term fix, so I have ordered new ones. But, for fun, I want to take the old one apart and see if it is fixable and will work properly. After a manual clean, I'll run it and the bits 'n pieces through the ultrasonic cleaner with some cleaning stuff I use. I also think that it's time to put a sediment filter in the line coming into the house to stop that problem, at least. I just bought 2 filters last week. One with the sediment filter and the other with carbon. I have those ganged and connected to the garden hose outside to reduce chlorine when watering plants. Sigh... so much to do.

What was the size of that nut, my largest socket is 1'-1/4" and is too small...