jerry, I would be interested in hearing some feedback on this as well as this tends to be one of my swing faults. I can tell you what has helped me...
1. Work on moving the left shoulder up instead of around to initiate the downswing. This will help prevent the left shoulder from moving over the top and spinning out too early. Additionally, the left shoulder up move may help you feel axis tilt.
2. Another reason you could be spinning out and bending the left arm is because you are aimed to far right. If you think about it, if you were aimed to far right, you would have to swing over the top (spin with the left shoulders) to get the ball headed to the target. And, an outside to inside swing may be the reason your left arm is breaking down.
I'm sure the true TGM experts will way in soon!