Hi,
I too, have had unstable Sternoclavicular joints for over a year now. I can't remember when this happened or what caused it, since there is no pain, it just pops out of place when I move my right arm, and makes nasty clicking sounds. From the research I have done, I can tell you that with this type of injury, the only option you have is prolotherapy. I have been looking for solutions for this everywhere for a few months now, and have found absolutely nothing. Surgery is out of the question too because it would limit the ROM of the shoulder so much that sports will be out.
I have just had my 3 prolotherapy treatments and still see no improvements. But I read that it sometimes takes months to heal. I will update this forum when I see improvements with prolo.