Thanks for reaching out.
Section 5, page 19 of the official GL1000 workshop manual recommends the use of “liquid sealer” but does not get any more specific. Plus, that information is 40+ years old.
Randakk's practice: Install OEM Honda head gaskets “dry.” They are impregnated with heat and pressure-activated agents to ensure a proper seal for the oil and coolant passages. Adding any “gasket sealer” to the equation might compromise Honda’s engineering and invite disaster.
Decide for yourself, but if you ever want to test this and waste $40.00, torque down a new Honda head gasket. Then come back the next day (without firing the engine) and remove the head. You will be amazed at how well bonded the head gasket is without the benefit of a heat cycle! Note: this “experiment” will destroy the new head gasket!