Coops (Pilbara) replied:

gearbox is best with a 75w/85, GL4 is what I have been recommended for my 96 80 Series. Should be similar.
This recommendation came from Russell at Synforce (Advertiser on this site) and you can contact him personally or order online.

Savvas replied:

Ferret,

You may have misread the manual and put in an oil that's too heavy.

Castrol's lube guide recommends VMX-M 75W/85. Penrite recommends Manual Gear Light 80W/85. Penrite goes on to mention good cold shifting characteristics with their oil.

Check their online guides -

Castrol's guide

Penrite's guide

fourstall2000 replied:

Ferrret,I have owned 3, GQ models,petrol and diesel,you must use GL4.
The tolerances are too tight in the gearbox for anything else.
If you use GL5 (even some Nissan dealership use this more common oil)
You will find gear changes harder on cold mornings,I have checked this with castrol and GL4 is specified and must be used in these boxes.
Regards

Russell from Synforce Lubricants replied:

ferret, 75w/85 GL 4 is the correct one for you, 80/90 is too heavy and GL 5.
we are currently trialling a more suitable gear box oil with some forumites, may be one of those could comment even at this early stage.
russell

Martyn (WA) replied:

Scott,
My book says 75W / 90 and I run a 75 / 85 in the GU, don't forget the Autran DX 2 in the transfer case, have you checked that yet? Sorry I didn't catch you last week the week just got away from me, are you back in again before Easter I'm off on Thursday.