The ATF "Label" is molded into the cap on mine, I doubt it's going to fall off! ATF is the Toyota recommended refill fluid, but the 80 along with most of it's era and older Toyotas come from the factory with hydraulic oil in it.
ATF is hydraulic oil with additives, most to deal with the clutches in the trany, these additives would be considered contaminates in a pure hydraulic system, which a power steering system is. My take is that Toyota specs ATF for refills for convenience reasons, it's readily available at all shops and will work if not pushed hard.
A lot of simple hydraulic systems allow for ATF as a fill fluid, more precision, higher pressure systems warn against it due to cavitation and varnishing problems. The groaning, whining sound from the pump is from cavitation, tiny bubbles form on the vacuum side of the pump vanes and implode on the pressure side. This implosion is very small, but has high heat and burns a tiny amount of fluid, converting it to varnish, it can pit the pump vanes and cylinder.
Ether fluid will work, but hydraulic oil is a higher performance fluid for this application, it takes more temp, pressure before it cavitates.
