The Case 580 series is a very popular model...
I would suspect that parts are still available and the machine is very capable...
Parts support for my dad's old IH 3616 is non-existent since IH construction has been out of business for sometime...
I think Komatsu purchased the IH construction division years ago...
If I was in the market for an older hoe the Case would be at the top of my list...
Things I would look for are leaks, leaks, and more leaks...
Check out the engine, hydraulic pumps, and look for excessive wear in the swing of the hoe...
These older machines are nice to have and can do a lot of work but do require lots of maintenance and can be a money pit if worn completely out...
5K is not an unreasonable price for a good serviceable machine...