The head gasket was leaking outwardly for the Avalon. An independent mechanic recommended selling/trading the vehicle, or continuously monitoring coolant levels and temperature. You could see coolant slowly leaking from the engine when viewing under the car.

Toyota dealership said it was no problem and did not recommend repair.

The challenge with the repair is making sure that after machining the engine heads, you have to find a gasket to compensate for what was removed to ensure timing is not off.