This has been hotly debated item on here, with posters saying Kubota has told them the 300 hour interval still holds. I split the difference and changed mine at 350 hours.
Will
I guess that would depend on the model tractor you are referring to? All Kubota tractors don't have the same service interval time for changing the transmission fluid. I have 5 Kubota tractors with service intervals ranging from 300, 400 and 600 hours. Best way to find out would be to contact your dealer or Kubota.
Is there a service bulletin for this?