As I suspected, Brego was broken. Although he was doing well on our rides, and eager to go, he just couldn't hold that left lead together. The chiropractor confirmed it today: left hip.
The good news is that she was able to get it mobile again and she flexed the hock and believes that it is clean and clear. She suspects that the hip was the result of his falls, and not necessarily favoring the hock. She did not seem to think there was any real muscle loss.
The bad news is that I dropped the ball. I should have gotten him to a chiropractor before the end of last season, certainly before he sat all winter. I am sad I let him down. I knew he was having trouble on that left lead and I let my finances dictate timing to get him looked at.
Never again. I will beg, borrow and/or steal to get the cash.
The chiro thinks there's no irreparable damage and Brego will be fine, but I still feel guilty. Any fall and he gets looked at, although hopefully we will not fall again. Additionally, I think I will get him looked at every 6 months until I am sure he stabilized.