Just slightly tore my rotator, not from paddling but Olympic overhead weightlifting so ... just hit the PT and rest/theraband deal.

If it continues to hurt I'd go to a SportsMed doc and get it xray and evaluated.  

You can do Theraband shoulder/rotator PT excercies year round to keep the joint stable.  They take a couple of minutes a few times a week and help a lot.

My wife (paddler) has very unstable shoulders and she has used regular theraband to keep the rotator strong and in shape when not paddling.

Sorry I do not have a link but they are pretty standard  rotator excercises-- should be able to locate a url.  

Good luck with it-
Jason