I have a 1420 combine. The hydraulic reservoir was nearly empty, but there was no evidence of substantial leak on the ground. I then discovered the transmission was absolutely full of fluid. I drained 3 gallons from the fill port on the side of the transmission. It seems hydraulic fluid may be leaking from the hydrostatic motor, through the drive shaft housing and into the transmission. Is this possible? How difficult are the seals to replace on the drive motor? Any special tools required?