Shift Cable

[Destroyer]

Whale.. this is just an educated guess, but since you say you can move the inner shift cable if you hold onto the outer jacket I'm thinking that the inner cable itself is ok and that somewhere there is a clamp that has let go/rotted/loosened up and is now allowing your outer jacket to move. Not knowing how the outer jacket was held in place originally prevents me from making any guess as to what is wrong. As to whether or not it will require replacing the assembly or simply tightening a clamp depends on what you find when you actually look at it.