I just changed the transmission oil in my Kubota L3000DT at a little over the 400 hour mark as suggested in the manual. The oil I drained out looked really good for being almost 8 years old. The thing that caught my attention was the condition of the strainer type filter when I removed it, it was pretty loaded with metal particles.
I priced the Kubota oil and it was $15.00/gal. for their UDT, the Super UDT was much more. I found that Amilee (sp?) has a product called Ultra Trans 245 that meets or exceedes the specs for both the Kubota UDT and Super UDT as well as several other brands, New Holland, Cat., John Deere. The price of the Amilee oil with my discount at the local auto parts store was $9.50/gal.
I understand the concern of using another brand of oil while under warrantee, I had the same concerns. I think most dealers would not question a warrantee claim as long as you used an oil that was better than the original brand. I found out the Kubota dealer I went through used a Castrol product for engine oil changes instead of the Kubota brand, so they make substitutions also but may not tell you.
Randy