Well, after looking under the bottom of the trencher, fluid had covered all the hoses, and I could not tell which had failed. Put my digital camera under there and took some pictures, and also felt all around, and I finally found the faulty line/hose. It was the steel pressure line going to the plow circuit, and that is why it was pumping fluid really fast. Anyway, I felt a lot of rust on the pressure line, and made a decision to pull the line and check for sure. Sure enough, that was the one leaking. Rusted through. My deduction on why the line rusted out was that someone had put a foam sleeve on the line to prevent rubbing, and I think water got trapped in the sleeve, and water/metal equals rust.
Well the bad news is that they can't make a replacement steel line, so an equivalent hose 32 in long with JIC-10, would cost $75 plus cost. NOT me. Ordered the hose from Discount Hydraulics for about 1/2 the cost.
I had raised the wheel off the ground with the bucket and the plow hyd, and the trencher was still up in the air three days later, so I am expecting good things from this trencher, with Backhoe.
The new fuel pump was dead so took it back to NAPA, and got another one, and put it on a battery before I left the store, and this one does work.