Gear oil or Hyd. oil?

I finally got my D14 running. I drove it around just a little and drained the hydraulic and transmission oil. I know that on many applications the manufacturers have changed the recommendation from gear oil to hydraulic fluid. My D14 manual states I need 80W gear oil, but is this one of those applications where hydraulic fluid would be fine, or perhaps better? One downside I see, the runnier hyd fluid might seep past seals a little easier, but might work better in cold conditions. There is no question that hydraulic oil will go back in the hydraulic system. Thoughts?

Edited by redline - 11 Feb 2012 at 11:39am

Thanks-I think she will have a date with the power washer sometime soon, but she showed far too much promise to give up on her. I eventually will have more questions on paint scheme and decals. I am quite sure there wasn't any cream color yet when this was produced, but the decals look like what it came with. I was hoping it used the decal style with the  model number in an oval and on the side tins. I find it to be more attractive, but probably should aim for authentic when I get to it.

That is a sharp looking tractor!  The attention to detail is amazing.