I shortened my paddle quite a bit, not one for half measures. I went for a 3 hour surf in small to medium conditions.
It took some getting used to.
Shoulder still hurt but much less. The second half of the session I used my wife's paddle. That was even better. Her blade is quite a bit smaller that mine.
So far it looks like a combo of shorter paddle and reduced blade will do the trick.
I'll shop around for paddles. My shoulder needs to recover and I'll give it some time. Then the changes to paddle etc should mean no more pain.
Thanks for all the help.