On a 753 Series F had to add 1.5 gallons of Bobcat hydraulic fluid to the chain case on two occasions after 50 hours of use. Do not see any fluid on garage floor or ground during operation. The upper hydraulic fluid is full and have not needed to add any hydraulic fluid. Where is the most likely source of the chain case leak? Do not see any sign of missing fluid on the wheels. The bottom of the bobcat has 1/2 inch of black grunge? Could leaking chain case fluid be absorbed by dirt in the bottom of the bobcat?