Gear oil is the wrong oil for any part of your machine, Some gear oils will damage bronze or brass, The correct oils should be listed in your manual. But I will say that most lathes in this class use a Mineral oil in the 10 to 20 Wt class of viscosity and have additives for wear and pressure. It is Generally referred to as "Turbine Oil" Many a lathe has been ruined by putting Gear oil for differentials and transmissions. If you put gear oil in your headstock also, Then your bearings in the headstock are starving for oil because these lathes work on a splash system to lubricate the headstock bearings, And the 85-90 gear oil will not splash up to the top of the headstock and ruin the bearings. I am not familiar with your machine and I don't know if your headstock has a Labyrinth style gearbox or not.
But it is always best to follow what the manual specifies when it comes to lubrication. Ways should use "Way Oil" also because using the wrong oil there can cause chatter.
I know about this from experience, I once had a lathe that I got for cheap because the Headstock was filled by the original owner with 90 wt gear oil, It fried the bearings and I replaced them.
This Lathe was purchased new by an old machinist who was accustomed to the old WW2 lathes that actually used 90 wt Gear oil in them. These newer lathes don't use it anymore.
