If it it a #6, go to a GM dealer-they are required in their Special Tools program to have one of these (we are a GM Dealer, and, we had to buy this Tool), and it will make a 3/8" (-6) o-ring flare on tubing:

Mastercool Inc., Flaring Tools

I wish you lived closer, as I fell in love and recently purchased it (ok, I admit it-I'm a Tool Junkie-where do I stand for the 12 step program?)-