The ultimate fix is to install a Timersert. Unlike Helicoils which are indeed coils, Timeserts are solid and use no more space than a Helicoil. Another advantage is Timeserts roll the last thread and using the special insertion tool that comes with the kit it forces the bottom of the Timesert into the parent material so it will NEVER come out. I bought the 10mmx1.0 for spark plug holes and the 5mmx.8 kits. They run about $65 for the kit and 5 inserts. New inserts run .85 each.

www.timesert.com