Replaced heater element.
Only hard part was divining how to access the heater without disassembly guidance. It'd be easy to do again now I know that first you MUST remove the doors. Then, after loosening the small cover plate just below the freezer the liner can be slid straight out to the front, revealing all. Except for waiting for the giant block of ice that you'll find there to melt, the whole process should't take 30 minutes.