On my 2009 4/4 the bottom bolt is the drain plug. It looks just like all the others around the diff cover plate but it doubles as a drain plug.
To refill I pumped it up into the fill hole.
i don't have a photo I'm afraid but there is a good illustration on https://www.gomog.com/allmorgan/btr.html#Filling

Good luck

Paul

2009 4/4 Sport in Red
2022 Harley Davidson FXLRS Low Rider S
1974 Honda CB450K7