My experience has shown me that with a 5" cylinder the pressure really isn't that high to get a log to split. Usually less than 500#. This explains how they got by with plumbing fittings. They are rated at 700, and probably explode somewhere over 1000. I would change them out.
Engine is the old style flathead. If it runs, use it. Less power than newer stuff. And 5hp really isn't that great anyway. Stick a single stage pump on it and then it really gets bad. 2 stage is the way to go. Swapping on a 13.5 gpm pump from Northern might not be that bad. I used this combo for a few years. It would split anything, but the speed was slow. If you are not trying to bust thru more than a couple of cords in a day then it will work fine.
They put the filter in the correct place. If it is in the feed line to the pump then it can restrict the flow to the pump causing other problems.
Get all that water out of there! It wrecks really expensive stuff.
-pat