I did have the fan blade replaced two months ago by Kubota dealer. Would they need to mess with the hydraulic fluid to access the fan blade (removing the radiator?)
I use a dipstick borrowed from a car and stick it down the fill hole to a pre marked spot at the top of the dipstick that lines up with the fill hole. I can then see where the level is at when I match the top mark on the outside of the axle case. I find that sometimes there is a bubble in the window and it makes it difficult to know exactly where the level is at.
Just my 2 cents.