<<Disagree. When I installed crossover tube on new 1.9L long block,
fitting in question got a new O-ring as well as plenty of the
copper-colored Permatex.
I have two years trouble-free operation to show for my efforts.>>

And you reused the collapsed old o-ring?

Bless your heart.

It isn't the accepted or proper way to do the job.

The ONLY accepted substance to be using, if at all is high tack.

Caterpillar uses, and suggests their own high tack on every o-ring joint
on any of their engine's.

NO Silicone.

The possibility of it slipping out of the joint / union durring assembly
is high.

And this practise is a good one to follow in any engine assembly.

The only exception to this rule is if you were using GM engine sealant
along with gasket's, which is the best of the best .
But this is in a gasket situation  not an o-ring.

You just lucked out.