Push the Aux button about 100 times. Blow it down with compressed air, spray contact cleaner on it.
Lay a block of wood on it, gently tap it with a hammer.
If none of that works, you have to take it apart.
Actually not sure about the volume control situation. But if the aux button is stuck down it will not let the radio fully function. Sometimes not even work.Would that cause the volume control not to work on the bars?