The bike is going to have to have an oil pressure test done on it .. there is a special fitting needed ..I will measure my fitting this morning when I get to work but I believe it is 10X1 mm ,Honda uses a banjo type with a quick connect fitting on it .. I have the Honda gage but I mostly use my Fluke PV500 & Fluke graphmeter to test the oil pressure..
The pressure is:
min. idle== 22 PSI
min. 5000 RPM ==116 PSI
I've put about 2 dozen hydrostatic transmissions in Rubicons and I've never seen 1 just not work without the operator not hearing/feeling something .. Even when the hydro transmission's rivets break off the squash plates you can feel the bike viberate as it tries to move ..