something else to try...I'd like to suggest if it seems like the left shoulder is "dropped" relative to the thorax and in comparison to the right side (secondary to poor neck function) as opposed to needing to stretch traps and lev scap, perhaps manually elevating the shoulder girdle (you can tape effectively under the scapula to try this) will unload the brachial plexus and can relieve symptoms in the arm inc swelling, neuro-vasc. if the taping works then strengthening deep neck flexors, rhomboids, central deltoid, and shoulder shrugs can do this actively.