Like many have said in their posts, I would not leave the corporate job. I have many friends that fly outside of part 121 and are VERY happy. You have to play the cards in your hand the best way possible. Your odds of getting a really good corporate job over time are WAY better than an industry leading 121 job. Reasons for this are simple. As guys have said, the past haunts you much more when applying to a 121 gig. The future of applying is all going electronic and despite how good of a person you are these application point systems will be hard on your past and their is little people can do to help you get past that. In GA flying they are all about you and your work history in the field most of the time, and since you have a good job there, I would hold on to that. Use it to build a great future for yourself flying in that environment. Part 121 flying isn't the end all of aviation and great jobs certainly are out there beyond the terminal or cargo ramp walls. Good luck to you!