yes - gear oil does reduce drag.
the drain and fill bolts are obvious - in typical Honda fashion the drain bolt is a 3/8 square drive. a 3/8 ratchet or breaker fits there perfectly.
the fill bolt is on the diff casing side.
Only drain and fill with car perfectly level, not on ramps or on jacks on one side.
You will need 3 litres of oil - fill quantity is 2.5 litres.