Re brakes, if you have hydraulic fluid leaking out from under seat area there is probably a leaky brake line. The brake lines run from under the dash along top of transmission, under the seat and into rear end above the axles. Remove metal cover off top of transmission and inspect brake lines. May have to remove seat and deck plate for access. To bleed brakes there is a grease like zerk bleed screw on top of each rear axle. Clean around bleed screw, with some plastic tubing and a clean container, warm tractor and let run abot 1400 RPM, fit tubing over end of bleed screw and let hydraulic fluid drain into container until there is no air bubbles, tighten bleed screw. Repeat on other brake bleed screw. If hydraulic fluid is clean, you can re-use it.
Re loosing power, junk in the bottom of fuel tank, you will have to drain tank and take the shut off valve out of both sides of tank, clean shut off valves and blow lines with air, flush fuel tank.