I don't like Loctite on headsets, but in dicey situations like yours where I lack good thread engagement, I use "vibra-tite" on the threads, which provides enough traction that I don't have to torque the locknut as tight as I would otherwise.
The advantage of vibra-tite or similar product over Loctite is that it allows readjustment if necessary without taking things apart to freshen the adhesive.
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