My understanding is
oil filter manufacturing companies will make whatever type of custom filter a company wants as long as they meet the minimum order amount and pay for them. I also have not heard of someone finding an "off the shelf" oil filter that matches a Kubota filter. At minimum, Kubota seems to have more pleating and more steel than other filters.
The Super UDT2 oil is similar, it heats up less and lasts longer than other oils.
Ashland makes it, and it
seems to be a custom blend.
Kubota seems to try to pack the most into a machine that they can, and I
think one way they do it is going above-and-beyond other manufacturers regarding lubrication. I've heard of oil other than Super UDT2 not cooling sufficiently and leading to excessive clutch wear.
I did find out who makes WoodMaxx oil filters for the presumably US-made hydrostatic unit, and those are off-the-shelf industrial high-filtration quality filters. I haven't put that amount of effort into researching Kubota filters since my local dealer has reasonable prices for the excellent quality product, and I'd
think someone else would have found a match by now if Kobota was using off-the-shelf filters.