Oil for rear diff - 4trak F75 1988


Can anyone recommend which oil (viscosity) for the rear diff of a 4trak F75 1988 having done 160k?
How much is required?
Is it worth using semi-synth plus additive?

I'm also thinking of draining the gearbox, as the gear change is stiff for the first few minutes on a cold day. So any recommendations would be appreciated (viscosity/amount/additive etc).


diff oils etc

Front and Rear Diff - 80/85/90W API GL-5 1.5 ltr (each)
Gearbox - 80/85/90W API GL-3 2.7ltrs
Transfer Box - 75/85W API GL-3 1.4ltrs

I found changing my oils made a lot of difference, less noise, better gear shifting etc.....

However, I have quoted you figures direct from the service manual - personally I use 75/85W GL-3 ESSO across them all and have no issue. But I have also added some Landrover (sorry guys) axle grease to my front axle to stop a leak on the ball joint.

Most good motor stores will have either 75/85 or 85/95W gearbox oil....if you want to save some money, do not buy it form Halfords or your local motorstore, find an Agriculture Dealer, they will have it in 25ltr drums.........at a sensible price.