When buying a new steering box you will find different values for your old core. I would look for a vendor that gives you the most for your old core. I have seen a core value of $90 +. Many years ago a got a new box from AutoZone and was only about $20 cash out of pocket after core return - that box is still working fine - no leaks. A Delco rebuild would be my first choice, but I would not spend a lot of money for it. Check the usual OEM suspects:
www.rockauto.com
www.oewarehouse.com
www.oehq.com
www.autopartstomorrow.com
ebay
amazon