Brim full at that street elbow with the pipe plug in it. (red arrow) or you can take the rate/cycle lever plate off and put the oil in there. (green arrow) About 1" to 1-1/4" below that plate. Just be sure to index the levers back in their slots in the control valve assembly
when you put it back on.
What are you running on the AUX ports? I am thinking there is only about 2 gallons or so in the reservoir. If you are using a single-acting cylinder you may be using it all.