If the gearbox uses a worm gear, I'd go with 90W Gear oil. The way lube would probably also work fine, as it's a formulation of a HP gear oil with an additive that makes it sticky. The downside is that more heat will be generated. At the end of the day, you could probably get away with banana peels for lubrication......
I think the advice was well intentioned,
but misguided.Would you change the oil
in the differential of a brand new car?