The issue is called Distal Clavicular Osteolysys, basically bone spurs and arthritis in the AC joint. The doctor called it "weighlifters shoulder", so, there you go. It was pretty obvious on the xray, even to a layman like me, that the space between the clavicle and the scapula was crunchy looking, not smooth at all. The arm motion that hurt was bringing my humerus in toward the centerline of my body, as if to scratch the opposite shoulder, and that is the motion of a BTN push press, only above your head and heavily loaded. So far a cortisone shot has been magical. I'm going back in two weeks to check on it.
No I don't consider the time spent on the BTN cycle wasted, the more you do, the more you learn, both good and bad. For me, I was using it as a main lift in the GSLP A/B rotation, and that was too much. I hope to use it as a supplemental lift in the future, cuz it's fun as hell to do!
Thanks for the response, I appreciate it. I'm kinda flailing along by myself (foreveralone.jpg as Brent would say), so any input is welcome. I went to go see a sports medicine ortho, by the way, because I wasn't going to accept "you have to stop lifting weights" as an answer.