Ok, so I did a bit of Googling and it seems these gearboxes are quite particular about what oil you put in them!
I drained the 80w-90 gear oil that Repco supplied and filled up with Amsoil MTF and it is completely different!
No graunching in second even from cold this morning.
I would recommend this fluid for your NV3500 gearboxes!
It’s even mentioned on the back of the container.
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