I'm not aware of a BX125 model tractor, might want to verify the correct model number.
I would start by trying to find a workshop manual (WSM) for your tractor at
http://kubotabooks.com/ or other source. Part numbers can be located at
http://www.kubota.com/part/partsList.aspx
Also, post some pictures of the area of the leak.
My BX2360 holds well over 3 gallons of HST fluid. Seems hard to believe that would leak through a damaged seal. I'm wondering if there is damage to the case or hydraulic filter is broke off, especially if the MMM hit something when it occurred.
Post some pictures, and best of luck with your repairs!