I have a what some call a trick shoulder, I think from my early days of sports and motocross. I have become very aware of what I do with my left shoulder. I put the accordion on my right knee and don't extend the left arm as much as I would if I put the accordion on my left knee. I can tell the difference after playing on either knee. Right is better from my shoulder. I don't do much playing standing up.
Thanks for all the replies about the elbow. I got a program from the trainer at my gym that avoids strain on that part (most bicep exercises are included). I'm going to consult a physio too. Friends whp play fiddle have told me about neck problems they've had too and how they approached it.