Ugh. No personal experience here either. Hope you get it resolved soon.

I would note (and this is very much my personal current experience) that the ENTIRE shoulder girdle functions as a unit, and if one thing is out of balance, nothing else will work properly; if one thing is out of balance for a long time, EVERYTHING is going to need correction. That's everything from scalenes and SCMs through the intercostals down to the diaphragm. They'll need to be targeted with myofascial release, stretching, balanced strengthening, possibly with direct manual realignment ...

Good luck.