Lucky me, my doc gave me the option of either surgery or therapy - I went with therapy. Don't believe you mentioned if your problem was traumatic or just old ... er ... older age. I did mine falling off a roof - that's more in the category of stupidity I guess. Tip to self - stay off roofs in winter - it can get slick up there. Mine was a 40%+ tear which is borderline for therapy, but apparently there's a whole lot of redundancy in the muscles. Went for it, and absolutely no problems since. Knock on wood, toss salt over shoulder. Yeowch?
Anyway. Stretch, stretch, stretch. Once you lose range of motion you're fu ... fu ... functionally impaired for good. Best tool for the job? Get a heavy duty closed pulley and hang that from a doorway. Run a piece of nylon rope thru and tie a couple handles to that about chest level sitting down. A couple chunks of sawed off broomstick drilled for the rope work well. You pull the bad shoulder thru with the good one, scream, repeat as needed. You can get all kinds of action on the shoulder by moving the chair around - front stretch, back, to the side, across the chest - just make sure you attack all angles and make it hurt without hurting yourself. Concentrate on the angles that give you the most problems - once those settle down, all the rest follows. Couple days, you'll be amazed the difference. Keep that rope handy and give it a go anytime the shoulder starts to stiffen up, which it probably will for a while, especially up there in cold country.