Is it a hole near a rear surface unit? Do you have the oven vent in the proper position or is it even present? If you lift this surface unit and remove the reflector pan, do you see a small pipe sticking up under where the rust hole is located? There should be an oval vent cover that goes between the pipe from the oven and the hole in the reflector pan under the rear element to carry away moisture from oven cooking. Rusting of the metal like you describe sounds like the oven vent is missing. Repairing the hole without putting an oven vent in place will not be a lasting fix.
