when i pull axles i always have a clean lint free shop rag ready
i put a pan under and as soon as i get the axle out i stuff up the tube with the rag then wipe up the little bit that got out
keeps things nice and tidy while you work lol
seeing youre a novice
remember to remove the rag when you put it back together lol
the axle fluid is pretty thick so youll lose only a tiny amount
i think this machine has a traditional diff with the fill level plug in the front if you raise the mast
you might keep looking for the "top off hole", maybe on the side of the differential housing, on the side were the input shaft is, not just on the outside.
and/or you could close up one side, lower that side, and fill the open side with gear oil until it ran out, slide the axle back in and tighten it up, lowering one side at a time...