I did a temporary repair on a thermostat outlet once. It was almost but not completely rotted at the outlet. I bought a section of copper pipe the same OD as the gooseneck ID [Aluminized steel conduit would have been better] and cut to length, inserted the pipe sharp cut end first after generously slathering sealant on the remaining piece of the original outlet. A good hammer on a piece of wood to protect the copper and the seal was made. Fill in the missing pot metal with Aluminum filled epoxy, let it cure [boy does it get hot] and file to shape. Then go looking for a real replacement for my RL411. A KIA SEPHIA unit fit just right and I am still using it. Even looks like the original.