<<Esteemed Sir,
Is this not only to keep the o-ring properly seated during assembly
rather than to act as a sealant? Inquiring minds want to know. >>

Yes Oh Noble Headed One.
Your right on the money with this assumption.

The Cat high tack is to hold the o-rings in place for proper assemebly
rather than to act as a sealer.

I wouldn't re use an o-ring if my engines were hanging from a shade tree
in the back yard.

They are plenty cheap and will do the job they were intended to, if the
mating surface is: clean , dry, and un-queefed up.

If the hose side ( which usually hold's the o-ring) is messed up.
Replace it prior to gamming it all up with silicone, gold , blue, black
or red.
It's all the same, and doesn't make for a good professional repair.

High Tack is a much better choice & solution.