Found a rebuild on eBay for $550 with valve. (free shipping)
Tested to 40psi
Hope it's worth it.
Worth it ? are you serious >>
as already stated rebuild your core .
A Heater core is just a tiny Radiator easy to core out and rebuild .
I have had many huge truck
Radiator's rebuilt with both tanks pulled ( top and bottom ) all re-soldered up for example for $125 and that's a large truck . Yes if you need a new core that's more money .
I did pull and reinstall the unit's . A Heater core should be about $30 to $60 to clean out and reseal up if you do the R & R (Remove and Replace )
Most often a leak develops along one of the tanks ( common Failure ) .
Leak stop poured into the Radiator well ruin a radiator by clogging the runners up but a shop can simply rod them out and re-solder the unit . Thus the word Rebuilt . Any good shop could do a Heater core clean out and re solder in 30 mins once in hand .
Heck if your rich just buy a new car .