Starting to show signs of hydro locking

So far you're just dealing with a dealership. Assuming you've already talked to their service manager without good outcome:

Round up all the paperwork, scan or take decent pics, email Toyota USA, explain as completely as you can.

Gasket Masters used to have a video, about dealing with stuck head bolts. They've taken it down, but it goes something like this:

Start turning bolt to loosen, and listen. There should be a distinct pinging sound as it breaks loose a bit. If you're not hearing that, place just a socket on the bolt, and give it a sharp rap with a small sledge hammer. Then try loosening again, listening for that distinctive ping. They call it "shocking the bolt".

Apparently dealership mechanics didn't know about that, leaned on it till the head snapped off.

 

No, it has not been taken down.