[dalola]

Cobralee,
If done properly, a Helicoil should not come out. Before using Loctite, you may want re-tap the thread, and try a new Helicoil of the known proper size. Remember, Helicoils use a specific , matching drill and tap. I suspect whoever did this initial repair used the wrong drill and/or tap, in which case, you may very well need to resort to unconventional methods. Also, a little anti-seize compound on the plug threads is cheap insurance!

Dave

P.S. In general, I would recommend Loctite 262 or 272, but you may want to confirm your application with Loctite, 800-562-8483.