Helicoil or timesert in your future.
On smaller screws I've just tapped the next size up. I do not know if there's enough material to go that route butt I bet there is. I could use my reference book to establish the proper torque to match the same tension.
If it was my car I think I would try that since the next step using helicoil will be to drill a similar hole used for tapping.
7, 8, 9?