There are plenty of diff oils to choose from depending on driving conditions, outside temperature and personal choice.

Driving conditions mainly affects vehicles towing heavy loads or work utes loaded up.

Temp involves weather you live in Hot darwin or cold old Tazzie etc.

Standard every day diff oil is about 85w90. If you live in a very cold envoirment you could go for 75w85 or 75w90.

If you have a loaded up work ute or towing very heavy loads long distances or live where its very hot then maybe go up to the 85w140. This is a very thick oil and if you have a worn diff it may prolong its life till you can afford to rebuild it.

Personal choice is just that and how large your wallet is. Synthetic or Mineral based, Home brand to Name brand 20 bucks for 4 liters or 30 bucks for 1 litre. Knock yourself out. Me I just use the standard S#@T we have at work Mobi Lube 75w90 cause its FREE.

Also be carefull using some diff oils in gearboxes. Some APL GL5 oils are not too friendly to the brass syncros in gearboxes. Best thing to do is decide on the brand oil you want to use then go to that manufactors website or google the oil you want to use and research its charictaristics. Most have a help line phone number on the bottle as well