Bill Hartman on shoulders (from t-mag article )
Got a problem with your right shoulder? Take a look at your left hip musculature. About 44% of people that have shoulder instability have a hip problem on the opposite side.
I know that this is not revolutionary, but about 5 years ago, as I was coaching swimmers, I realized that a huge key to reducing shoulder issues was not to do endless external/internal rotations, but to hit shrugs, overhead shrugs, Kelso shrugs, dip shrugs, pulldown shrugs etc. It had an almost immediate effect.

Over the past year, with the hip/hamstrings issues I've had, I realized that the hips too could affect your shoulders. Thoracic flexibility was another... I read something very interesting at dragondoor - it was something like the following:

Your musculature is like spokes on a wheel. If one is too tight or too loose it will affect the entire wheel.

Food for thought.