Don't give up too soon. All you need is Edger2.
Since both files should carry its own edge lines, all you need to find is the triangles and quads that make up the metal part, all in colour 494, and move them to a separate file, and apply Edger2 to it. It will create the missing edge lines you are trying to find.
But yes, you also need to find the unneccesary edge and condlines in the parent file, but that shouldn't be too difficult in MLCad.
Since both files should carry its own edge lines, all you need to find is the triangles and quads that make up the metal part, all in colour 494, and move them to a separate file, and apply Edger2 to it. It will create the missing edge lines you are trying to find.
But yes, you also need to find the unneccesary edge and condlines in the parent file, but that shouldn't be too difficult in MLCad.