Lubrication of 4WD U-joints on MF 2660

[JWR]

I have around 350 hrs on this 2011 low-profile, 81 horse, open station utility tractor used mainly for pasture clipping, bush hogging, and loader work for removing debris and limbs/logs while cleaning up a hilly old 100 ac farm. I use the 4WD a high % of the time due to steep ground and frequent need for more traction than any 2WD would have.

Any of you ever lube the U-joints on the shaft that drives the front wheels (of any model tractor?) How often ? Ever see bad outcomes of NOT doing that lubrication ?

I am somewhat surprised that the joints are not sealed or permanently lubricated given the function involved.