Here's a video you may find to be of some value:
The only reason I watched it is because it was there when I went on YouTube. I thought it would be just more of the same because I've watched a number of shoulder problem videos. However, this guy suggested to work the lat area. I felt no pain or discomfort in my lats at all even while working out. But I tried it. The upper lat below my bad shoulder and along the "ridge" was incredibly sensitive whereas my lat on the other side had no such discomfort. It was an eye opener. Since starting the ball rolling thing, it is a bit desensitized, but there is still work to be done.
Eye opener #2: The thoracic spine. He suggests getting on a roller to address that area because it has bearing on the movement and position of the shoulder blade, which in turn affects the shoulder. Again, I've had no issue with my upper or mid back whatsoever. But I decided to give it a try. Since I don't have a roller (I may buy one this weekend), I used my trusty lacrosse ball right on the spine and the erectors. I unintentionally used a bit too much pressure, because the pain was almost breathtaking, more so in some spots than others. I was very surprised, since I didn't think I had any issues there whatsoever.
I've been working these 2 new areas since yesterday, and the pain/discomfort has dulled down a bit. I plan to continue.
If you decide to give the lats and the thoracic spine area a try, let me know how it goes.
Oh, and you have the same ball that the guy uses. Perhaps you're related.