I've been run over by a car, popped my shoulders out plenty of times, and had massive tendon scar tissue...
I couldn't train very well at all for almost 2 years. I went to over 7 doctors and they all told me I was fucked....
Heres what I've done to get my shoulders back to 95% of their previous copacity...
1.Deep tissue massage.... You probably have OODLES of scar tissue surround your scap, on your bicep tendons, seratus, teres minor... If you have limited mobilitiy I would be willing to bet a lot of it has to do with scar tissue.... You are going to need at least 5-10 sessions before you notice BIG results.... I credit this to at least 75% of the reason my shoulder has recovered. 100% of the reason i can bench again.
2.Stretch. Lean against a wall, and pull your arm across your body with your other arm. MAKE SURE YOU KEEP YOUR SHOULDER FLAT AGAINST THE WALL... if you pull it forward it won't stretch your scap. My sports medecine doctor told me to do this stretch 6 times a day. 3 in the morning when you wake up for a minute each, and 3 at night for a minute each.... I also tossed in random 30 second stretches while driving... This really helped as well.
3.Cuban Rotations and external rotations(like you've been doing)... I've been doing cuban rotations for a while now... and even though they feel like death while doing them, my rotator cuffs have become incredibly strong compared to what they used to be... concentrate on getting 10-12 reps... when you can do 3 sets of 12, go up 5 lbs and continue your progress FOREVER... if you want ot get stronger your cuffs need to be there to back you up...
4.Chiropractor, you may have some subluxations in your upper spine cuasing your nervous system function inproperly. A simple adjustment can give you significantly more pain free Range of motion....
Anyways.. this is coming from a guy who couldn't even lift my arms in the air without extreme excrutiating pain, and is now pretty much restriction free with my shoulders. I was under the immpression that heavy training would never be a part of my life EVER again.... I have proven so many doctors wrong and I have never been happier....
I hope that gives you some where to go with your shoulder problems..
Thanks