Transfer gearbox oil

Been using tractor universal oil in my 300 TDI. Is it ok to use it in the transfer gearbox.? It is 15w 30 and has API GL4 which is what Haynes manual says it should have.

For LT230 a 75W90 oil is recommended or eventually EP80/90 (GL4 or 5)

As sierraferry says, 75/90W hypoid gear oil. Readily available and relatively cheaply from your local agri merchants or if you have a plant and machinery yard near by then pop in there with an empty 5 gallon can and ask to exchange beer tokens for some out of their bulk tanks, we used to buy transmission fluid, engine, hydraulic and gear oil in bulk as we got through thousands of litres of it every year.

Thanks for the info guys.