I use Iridium plugs and they have the screw-on nipple as well. Took them apart, hit them with Loctite and tightened them back up. A also squeeze the rubber insulator on the female lead to increase tension.
As for the comment about Loctite being an insulator it really doesn't matter. If it's tightened down tight enough there is adequate metal to metal contact on the threads alone. The Loctite mostly fills the voids.
With this car, Loctite is your friend and faithful companion...
