Please read post #8 above. - Both the implement pump and the powertrain oil pump are mounted on, and driven from, the back side of the torque converter housing. If the hydraulic implement pump was leaking through the shaft seal the oil would end up in the torque converter housing, from where the scavenge pump would return it back to the transmission case. In those circumstances the level of the transmission oil would be rising.
To quote your OP - "Very little external leaks although does go through some TRANS fluid."
Like Bloux asked you earlier - are you SURE it's not transmsission oil..? Because the design of the system makes it very unliikely that it is hydraulic oil.
How much is the level of the hydraulic tank falling.?
And if the engine oil is black (or at least fairly dark), as it normally is on most diesel engines, what are you using as a test to determine that there is an additive from the hydraulic oil in it..?