I can't speak directly to the TU1400, but I have a TU205 and the rear gear lube and hydraulic oil share the same sump. The TU205 has a dip stick in the fill cap located under the seat. We use a typical TDH rated fluid (Transmission, Differential, Hydraulics) available at any John Deere, Kubota, Cat dealer or everyones favorite, Wal-Mart.