My ducts were warped almost closed. I had my windshield out for repainting so I took the opportunity to address this condition at that time. I made wedges from wood, heated up the ducts a little at a time with my commercial grade heat gun, and inserted the wedges into the defroster slots, while hot, to expand them. I let the ducts cool overnight and removed the wedges. My ducts are back to factory appearance and shapes. May not last but they won't be out in the sun like the first 60 years. I do like that metal "fix" described above, though. I'll bet a supplier could use one of those digital parts copiers by using the first metal plates as patterns.