Hi, I just read back through your post and think that you are probably right- if that's the location that gives you pain and its quite isolated with hammer curls then it most likely is brachialis. I would say that you best bet is to begin a gradual strengthening rehab program- so start with the hammer curls but at a weight that you can tolerate with absolutely no pain and with high reps. You can gradually progress from there Also try some internal and external rotation exercises with light resistance (eg theraband or 1-2 kg wts) in case there is some rotator cuff damage.