[Houston54]

That area rots out because the brace is a hat section channel and traps all the dust/dirt at the lowest point. Of course it absorbs and hold moisture so this rots the brace out from the inside. It is a fairly easy fix with the hood off the truck. Remove all the rotted material, treat the inside area with a rust converter and prime/coat the heck out of it once that drys. Then weld in a replacement metal piece and grind to taste. Just watch the heat build up as it will warp the hood skin.