The Helicoil would make the best repair providing stronger threads than stock. Rethreading to a larger size is an option too but no matter how you do it you'll have to cut new threads in the alloy. Like kawi_klr says make sure the tap is started perfectly straight...once you have it started straight, thread it in a turn and then turn it back a half-turn to clear the chips. Every couple of turns unthread the tap and clean out the hole with a Q-tip with a blob of heavy grease to remove the chips. Make sure the hole stays clear of chips and when the tap approaches bottom be careful you don't bottom out and tear the new thread. A little WD40 or "Easy Tap fluid" in the hole as you go will help a lot...keep it wet.
Sparkle