how can i fix my kubota kx61-2?

have recently had the track motor go on my machine,took it apart to discover it was a center gear cog[dont know official name]had worn away,the drive motor was working and turning but had no thread to turn on,got the part fitted it but now the drive motor isnt functioning cant have put it back together properly but dont know where i have gone wrong.the oil is just pumping straight in and back out the motor and is not turning.any advise diagrams or photos would be helpful thanks