That never happen to me with my Kubota, but something like that happened maybe 15 years ago when I was using a Farmall 200. While baling hay, I was confronted with a sudden loss of hydraulic fluid level but with no apparent leak. Since clouds were thickening and rain threatening, I had to continue with the haying, so I kept adding fluid until I was done. When I got back to the shop, hydraulic fluid was coming out from the strangest places, including the starter motor. I found that the shaft seal on the hydraulic pump failed, overfilling the crankcase with fluid. The volume overcame the crankshaft rear seal and filled the clutch housing with fluid until it came out the starter. What a mess!! I don't know if such a thing could happen with your Kubota, but it could be easily detected by checking the oil level in your crankcase. The replacement seal cost only a couple bucks, But the cleanup of the clutch was, lets say, somewhat labor intensive!
Frank Z.