I ripped a piece of something there about three years ago and it has only begun to relinquish it's hold on me. I was able to continue paddling by taking at least one Ibuprofen before putting in each day. the doc said it was an inflamed bursar sack, a small fluid filled cushion that your shoulder rotates on, it gets inflamed and swells. Ib actually reduces pain by reducing inflamation, so this is actually a decent way to reduce the effects of overuse... personally, I feel that it was what Dave had, where the tendon/ligament (whatever was torn) had to pass thru a constriction as it went from my back to my bicep. I could feel it squish up and sqeeze thru sometimes!!
another way I lessened the pain was to move my hands in closer together on my paddle, try to keep my elbows "pinned" to my sides, and NEVER HIGH BRACE!!
(we hear that all the time, but when the river grabs ya, it never sticks!)