5 Speed requires Toyota WS, which is basically synthetic Dexron 6, most good makes of D6 will cover World Standard.
I too would change it, several times as TONYCY11 says , if you have the 5 speed you will need some form of oil pump or syringe to get the new oil in because they removed the dipstick and there is no way you'll get normal oil bottles near the filler plug.
Not sure what the standard fluid is for 4 speed, early 120's i believe do have the 4 speed and nothing wrong with that at all, no more difficult to check levels and change the oil than an engine oil change.
That Aisin fluid linked, if i read correctly states it's not WS spec.
Gearboxes that require WS will find WS stamped on the filler plug, which itself takes some finding being half way up the side of the box, offside of box if i remember right.