I have a 320B cat excavator once after working for awhile get strong hydraulic smell no leaks. I assume it is coming from the cap on the hydraulic tank that has a tube on it its like your rad cap is this normal.
I get exactly the same thing on my Case with 2600 hours. No leaks, just get a good hydraulic smell for a short time and then it's gone.
mine is there all the time when it gets warm can't smell it if i have the door closed and air on.
The filler cap (hex headed, around 1-3/16") has both an Oring seal and a brass washer under it, for to seal it. Is yours all there? 15, 16, 17
As the tank heats up the cap relieves excessive pressure just like a radiator , you have a good nose I've had "operators" dump 100 gallons of oil and not smell it. Bob
I've got a damned good nose for hot hydraulic oil, too. And a lot of Caterpillar machines. I never smell it unless it's leaking (and hot). First hunch...seal and/or ring under the fill plug. 2nd hunch...running something unique or odd as an oil.
Yes mine is all there has a rad cap on cap were you tank screen out as far as oil not sure what previous owner ran in it temp on hot 140
You might pull that cap and check it or better yet just replace it. Bob