Not sure if this will be relevant to you but I'll let you know about the problems I had with my shoulder and hopefully it will be of some help to you.
I suffered a trauma to my right shoulder that I then aggravated in the gym which resulted in acute tendonitis of one of the rotor cuffs and I think there was some damage to the supraspinatus as well. I carried this unjury on/off for well over two years and it really p***** me off as it would seem completely healed and then a very minor twist/bang the wrong way and it would flare up again.
What was happening was this: the damaged tendons would become inflamed as they tried to heal, but the space available to the various tendons in the shoulder is very limited so the inflamed tendons would rub against thier neighbours bones cartilage etc, the inflamaton would get worse as a result of this rubbing, the tendons would then rub even more due to the increased swelling and the vicous circle continued.
Although you haven't got the same thing I expect a similar vicous circle has led to your injury reaching a point where it is untennable - hence the op. As you heal after the op you may find this is a problem too - especially if you tweak it during recovery.
The way I finally got rid (fingers crossed) of the injury was: treatment physio to repair the damage (ultrasound, tens etc) followed by anti-inflamatries after each session. Once the shoulder was usable again an excercise program to recover the strength plus excercises to re-educate the muscles around the whole area. This re-education was really important as I had had the injury so long that I had learned to protect it and wasn't moving the joint correctly. This meant some muscles never really recovered the strength properly (I felt strong but I was just compensating) and this was why I was getting re-injured. Throughout this whole stage the use of anti inflamitories was crucial. I used mostly ibuprofen gel after excercise (not before as it masks pain - you want to feel it if you are trying too hard and doing damage). There were times when I had overdone it but the anti-inflamatories stoped the vicous circle before it started and prevented a major set back. After a while I learned when I needed the anti-inflamatories and when I didn't.
With regard to spearing - you will use the suprasprinatus loading your gun although it is not the main force generator obviously. It is more of a control tendon but that click over the notch requires quite a bit of control - what you want to avoid is dithering around trying to find the notch at high stress. I tweaked my injury doing exactly that! I would definately recommend slackening your rubbers for a while (if your kit allows - maybe swith from 1x20mm to 2x16mm?). Also holding the gun out as arms length when aiming/swimming is a classic movement that will aggravate the s.s. A well balanced gun will reduce the strain a lot - you don't want to be constantly trying to hold the gun up. Most Rail/Euro guns tip down a bit even if they are overall neutral - you could try adding a little float down the barrel like I have seen on some sporasub guns.
I hope this helps. Good luck with the op and the recovery.
Graham.
