I've not had shoulder pain, but have had persistent pain in my elbow and ring and middle finger of plucking hand for a long time, and the situation improved greatly when I cut all added salt out of my diet (which was and continues to be vegan non-processed). Was hard to do but the benefit only took a few weeks to appear. Seems like salt, among many other foods, can cause inflammation. Of course it is unknown whether it would help your condition.