I find the Kubota manual a little confusing on antifreeze as well as other subjects. My B3030 also has the expansion tank with green coolant in it. Ethylene glycol coolant used to be known as permanent many years ago. I can only guess they mean the standard green ethylene glycol coolant. All the extended life coolants I've seen are red,orange,golden,anything but green. Of course,I've seen red and tan regular coolant also in imports. I can appreciate your quandry. It's also interesting that they suggest a mixing ratio of no more than 50%,and list 40% and 50% freezing points in the manual. It's always been pretty much standard practice to mix green antifreeze 50/50 with water(distilled or de-ionized prefered) for -34Fprotection. Although I can remember cars coming with -20F protection from the factory,with -34F an option. My first car was a 1961 Impala that had the original window sticker with it showing antifreeze a $6.00 option.
Sorry to ramble-I think for lack of any other info,just use regular green 50/50. Good Luck
