Kubota says use their fluids
Any disadvantages to not?
Machine is not under warranty

Wouldn't think so... there are only so many refineries...

I have used non-Kubota hydraulic fluid during regular maintenance changes with no issues. It depends how much money I have when a scheduled change comes up. Kubota Super UDT is expensive!

they all say use their own fluids.......

I have a friend who has a Kubota dealership and he said when under warranty use Kubota oils. If you have a warranty problem the first thing they will do is take a oil sample

Dealer I bought my zero turn from said it was hokum.

What coyote said. After warranty runs out use a good name brand fluid. Eric

All manufacturers have oil produced by different refineries with the additives required for the brand. If I remember correctly the Kubota’s with a hydrostatic trans. call for synthetic hydraulic oil. I don't see how saving a couple bucks per gallon of oil vs. replacing a trans, hydraulic pump, or a control valve would be cost effective.

I have two Kubotas that have Napa hydraulic fluid in them and rotella T diesel engine oil in them right now. Sometimes I use the Kubota filters if im close by a dealer, have used the Napa filters as well with no issues