Try a physio who is familiar with swimming injuries. This is a common swimmer's injury. The rotator cuff's job is to keep the shoulder "together", not to do hard work - ie. it is a positioning job. Swimmers get into trouble when they over-use shoulder muscles in their swim stroke. A good swim stroke should get it's power from trunk muscles - large and powerfull. This is basic core stability stuff. If you train for a stong, stable core then the shoulders will have very little to do.
Hope this helps.