it's pretty easy to blame sloppy form but it's not the only problem...

rotator cuff problems are very common in swimmers and can be brought on simply through lots of swimming, i'm told at least, maybe some people do enough swimming for that to contribute? i actually think that all the impacts we put through our shoulders aren't too good for flexibility... a few years ago i had a guy look at my shoulders while i was being demoed upon for sports massage, and he said he could feel lots of muscle fibres that were getting, um, the equivalent of callused? starting to act like ligaments within the muscle, he thought a lot of impact might have been causing it? maybe another area we dont know about, maybe i'm a freak. off topic...

secondly, we've actually found that in particular practicing inside edge passing can contribute to these shoulder problems... we have had a few guys develop big inside passes and the shoulder problems carl has described at the same time, and only in the playing shoulder. passing like that takes strong muscles but when you are practicing, if you bother, it's important to do extra work on your back and shoulder muscles to counteract the training you are doing in the pool, just like the balance between push/pull muscle sets you do in the gym. it's just easy to forget that sometimes the work we do in the pool is actually causing muscular development (as well as improving technique) that needs to be balanced.

i might try your jerks carl, if it's as miraculous an all-in-one as you claim. sounds good!