If you have removed the primary cover and the compartment is dry, just put a small amount - a quarter pint or so in there, as it shares oil with the engine. Put the same oil in as for your engine. Do not use ATF !!! Also, don't forget the gearbox has its own oil, not shared with the engine or primary, I have had more than one Crusader type machine brought in for work, which has had a dry gearbox.
B.W.