Two places: Either the front seal is out of the hydraulic pump. Second choice is the seal for the draft control rod is bad  and you could have a hole in the pan itself.  First question: If you fill the hydraulic unit to a given level and measure it will it go down if it sets a few days without running the tractor? Take your transmission check plug and see if the oil level is high. If so drain it down before you ruin the brake seals.