Back in the day, with new parts and straight surfaces, gaskets were assembled dry. They would eventually fuse to the surfaces, prevent leaks, and be a bear to remove. On our own bikes, knowing that we would be constantly tearing them down, we would put a thin coat of grease on the gaskets. Easier to disassemble, saves on gaskets (can be reused), and the 'perfectly dry' appearance wasn't as important to us.
In a problem situation, like with damaged surfaces and chronic leakers, gasket sealer could be used.
Otherwise, it was avoided.
Non-gasketed surfaces, like case halves, did get the 'goo' treatment...