Pulled into the driveway, got out of the 'Sploder, and the smell was... well, obvious. And there was steam coming from under the hood. Opened the hood, and discovered this little beastie was leaking and dripping coolant directly on the hot exhaust manifold.
This is the heater control valve.
On an off chance, I took the dog for a walk by the neighborhood NAPA to see if I could get a replacement valve.
Took the old one out:
Put the new one in.
Remains to be seen if there is more to fix, but I turned on the heater full blast and didn't smell coolant. That's a really good sign.