If the system has a loose screen in the sump under the seat in the hyd suction line it will (even when pressurizing the sump) not suck fluid as the air will push into the pump suction in place of the fluid.
Other thing is to crack the line at the pump inlet and see if pressurizing the sump pushes out fluid.
As for the pump, yes two bolts hold pump to engine AND keeps the 3 parts of the pump together and the other two bolts just hold the pump parts together. NOTE: these bolts are not super tight as the pump has to turn but the gears and body are almost exact same size (very tight clearances.) If the bolts are too tight then the pump may actually bind up keeping the engine from turning over. There are rebuild kits (o-rings) that you can also rebuild the pumps with. Again you have to leave the pump shells loose and then start to tighten them some to make the seal without over tightening them locking the pump...
Mark
