I just replaced the axle seals and lower and upper seals and a small bearing on both sides of the front of my 1610D. All parts were approximately $150 US, plus a $50 parts manual that has somewhat useful exploded views and part numbers.
When you take it apart, be sure and not the position of everything and watch for spacers, bearings, etc. that may fall out. Make a note of where they went or identify them on the exploded view if you have one. Lay them out in the assembly order and keep them that way throught cleaning and till reassembly.
The axle sleeves had grooves worn on mine and instead of buying new axles ($192 ea from Japan), i opted to install a product called Speedi-Sleeve ($40 each). See
http://www2.chicago-rawhide.com/speedi_sleeves.htm for general data and
http://www2.vsm.skf.com/Files/Brochures_in_PDF/Speedi%20Sleeve.pdf for size selection. Maybe you can get a similar product there. Also, someone on this web site may sell a product specifically for your tractor - but Im not sure if axle sleeve machining will be required. If the speedi sleeve is available in the correct size, no machining is required.
I also put 140W gear oil back in mine as the large housing seals also had a rough surface that i could not smooth up. So far - no leaks.
You might reduce the leak rate by putting 140W gear oil in till you get it fixed. I dont believe it will hurt anything as these are low speed applications.
Good Luck
George Underwood