If it is coming out under the radiator, and not under the pump, or where the hydraulic manifold bolts on, I'm guessing the seal is out on the fan drive pulley, in the timing gear cover, or timing gear cover gasket is leaking... I'd lean towards the fan drive pulley seal. There is a hole in the front casting, where the radiator drain comes through. Guessing that is where the oil is coming down through.
If it is definitely hydraulic oil, I'd say the front seal is out of the hydraulic pump, and putting hyd. oil in the crankcase.
Do you need to refill the hyd. reservoir frequently..?? If so, could be the engine oil pan could be over full, causing it to come out around the fan drive pulley seal. Or just diluted engine oil, thinned enough to leak easier.
You can always set a drain pan under the upper petcock on the oil pan, and open it up, to see if the oil pan is overfilled. If setting level, it will drain down to the proper full level. Not sure I'd want to run it too long, with the engine oil diluted, if that is the case.
If the fan drive pulley seal is leaking. You'll need to drop the front end, to replace the seal. Some blocking under the bell housing, and something to hoist the front end. That will require removing the radiator, etc. You'll need to raise the engine a bit, then slip the front end out from under/behind the pulley.
In another thread in this section, Soundguy has some pictures of him removing/installing the fan drive pulley. A bearing seperator, and puller are just about a must. And check for a set screw in the hub of the pulley on the backside...
Not as bad as it sounds, once you've done it a few times..., LOL...
The hyd. pump seal is an easier fix, but let's determine exactly what all is leaking first...