Mouse Smell In Ducts Over 1 year now - will it sell?

My mother had the same issue with her Toyota Carolla. After tearing the interior apart, we took it to a mechanic friend. He had a scope camera, and found the dead mouse in the air vent under the passenger seat. Unless you can find the dead mouse, it is pretty much impossible to get rid of the smell. It is almost as hard as trying to sell it smelling like that. Ask me how I know.