Quoting my Ford I&T Service Manual (FO-46) for a nonsynchromesh 12 X 4 gear transmission, model 1720; "The transmission housing and rear axle center housing serve as a common reservoir for gear lubricant and oil for the hydraulic system. The oil should be drained and refilled with Ford 134 oil or equivalent lubricant every 300 hours of operation". You can use Super Tech Heavy Duty Tractor Hydraulic and Transmission Fluid as it meets the Ford New Holland ESN-M2C134-D requirements Super Tech Heavy Duty Tractor Hydraulic and Transmission Fluid - Walmart.com