From your model number it appears that your tractor does indeed have a sealed transmission. No additional oil should be required and the unit is not servicable. There are a couple of seals that are replacable but that is about it.
Please note: I am terribly sorry but I answered the above before I realized you would have to pay again to see. This is what the answer says and you have already paid. My apologies. I'm new to this Just Answer system and still trying to get used to things. Images available only to Customers.