Just saw your post. General answer is in the old days Ford had 3 sumps, tranny, hyd, diff. Then in the mid 60s they went to 2 sumps, tranny and hyd-diff combined and used hyd fluid with special additives for the combo. Then comes modern tractors with common sump for all 3 functions plus hydro. steering, plus wet brakes that never need brakes nor pads and if 4wd a forward sump at each wheel interconnected through the common drive diff and shaft.
Usually the fill plug for a sump is over the sump somewhere, at the top of the general casting. Full for any gearcase is never full. It's usually half way. For older equipment, FULL plugs would be pipe plugs of ⅛ to ¼ inch or a dipstick. The full plugs would be located about half way down the side of the casting involved with threads directly into the casting to accept the plug. Pour fluid in the fill hole till it runs out of the full hole.
For what fluid to use, a Ford 134A or JD 303 which is a trans-hydraulic fluid for older equipment without hydrostatic steering and wet brakes and all that newer tractors have to go along with their common sump used for tranny/hyd/and diff. For the newer tractors with such, I just look for the JD 20C spec which usually appears if anything does and if it's there usually the Kabota UTD is too and those 2 specs seem to cover everybody's equipment. Another thing is that the latter is usually referred to as "Premium Trans Hyd Fluid" and a lot of times it's dyed a faint orange to identify it from the 303 type oil.
