check your manual.
I have a 1957 model to-35 and it has bronze bearings in the trans.
You want to protect those transmission bearings. My older machine came with GL-1 mineral oil, they sell that oil, at a reasonable price, at napa or they can order it.
some use 10w40 oil in the trans/hyd system. I guess the new oils will protect the bronze transmission bearings.
just remember you must use an oil that will protect those bronze bearings in the transmission, if your tractor model still has them.
i assume they got smart and did away with bronze bearings in the newer tractors.