Damn the bad luck
The left handed bits do work real well. I used to be a forklift mechanic and nothing gets frozen in like bolts on forklifts, especially ones that run outside. I've had my left handed bits back several bolts out on them. By far the best $30 I ever spent. I've found the way clhyer said to do it works the best.
BTW: Don't helicoil it. It'll leak like a sieve. One of my heads had the threads stripped when I got my car and I tried a helicoil and nothing would seal it up. I finally took a 3/8" stud to a buddies and used his lathe to turn down one end then tapped 5/16" threads on it. Worked like a champ.