Single pump, open center hydraulics. Not as high performance as a closed
center system, but much cheaper and simpler. You can probably replace
the pump entirely for a few hundred $. Of course before you replace the
pump be sure to check the relief valve since if that has an issue it's
like $25. I got a small tractor with loader that had poor hydraulic
performance and all I had to do was clean and readjust the relief valve
to fix it.

Maybe I'm a pessimist, but I'd be prepared to drop $3K or don't start.
of course this is to get it back like new - rebuilt pump, new fluids,
new filters, new guage, relief valve, and a few other gotchas that
always come along (like hoses that will pop right away, cylinder seals
etc). I've repaired a LOT of tractors and the costs are always high.

Karl