Wow, I don't feel quite so alone anymore. I went through something similar, although I didn't have it as bad as you. I couldn't shake hands, lift a grocery bag, or drive for quite some time. The doctors I saw were stumped, and I got the sense that no one wanted to deal with it. I went to a PT, who guessed the problem incorrectly (in hindsight), but whose recommended exercises fortuitously happened to also help with TOS. It wasn't until many years later that a sports medicine doctor mentioned TOS as a possibility and everything clicked.

Can I ask how you were able to determine there was scar tissue? Was it just someone feeling it out or did you get an MRI?