The transmission is not sealed and unserviceable as you say, i own one myself and have just replaced sump gasket and filter, there is a fill cap on top of box and instead of a dipstick there is a level plug (11mm) located on side of box next to exhaust accessed from underneath.this is checked with engine running in park at operating temperature on a level surface. you add or drain fliud to this level. Fluid type is dextron 3. Amount is 11.5 litres dry or if you have only removed sump it takes 6.5 litres as some oil is retained in torque converter and internals of box even after sump is removed.

انا دورت بعد ما زميل سألنى على الكمية و قاللى اخر مره حاطط 11.5 لتر فيها
ايه رأيكم