Yes, this common facia warping problem can be corrected without removing the facia for less than $20. I used wood fluted casing 3/4" x 3 1/2", 3" blue painters tape and 100% silicone rubber caulk which can be found at any home imprrovement center.
1. Cut two pieces of the wood casing just long enough to span each side within a inch or two from the ends of each opening
2. Trim each board 1/2 inch to 3/4 inch along the length of each piece so that the board does not show on the open side when fully inserted into the facia. Test fit on each side and trim as needed so that the wood is flush with the rear of the facia opening. The goal is to span 75% of the middle sections where the sagging is occuring with each piece of wood casing.
3. Spray windex or other general cleaning product on paper towels or rags and clean the inside of the facia area where the sagging is occuring. Make sure the inside areas are fully dry before proceeding.
4. Liberally coat one board on top and bottom with 100% clear silicone rubber caulk (caulking aisle). This gets messy, so have plenty of clean rags available for your hands. Good idea to wear latex gloves for this step. Spread the silicone on the casing so that it is evenly coated about 1/8" thick on 100% of the casing board surfaces, all sides and ends.
5. Carefully push the wood casing with silicone through the top opening of the facia opening towards the radiator being careful not to get silicone on the radiator.
6. Push casing into the grill section from the rear while spredding the facia with one hand until it is fully inserted. Some of the silicone will push out to the rear, no worries.
7. Remove all excess silicone with dry/clean rags from the painted surfaces. Leave a thin layer of silicone on the back side of the opening along the length of the casing to form a water tight seal.
8. Using several pieces of 3" painters tape, start at one end and wrap the facia tight around so that the facia takes the shape of the wood casing. Work the pieces of tape next to eachother to completely wrap the facia opening tightly, but evenly from one end to the other.
9. Repeat for the other side.
10. Wait 24 hours for the silicone to dry and remove the painters tape. Any remaining dried silicone residue can be rubbed off painted surfaces with clean dry rags. Wax or polish the facia area and your job is done.
The silicone caulk waterproofs the wood casing pieces. This repair should last for years. Good luck!
