First, can you get the core out of the heater housing and actually find the leak? There are sealants available at NAPA which might work if the leak is small and easily isolated.
Second, is there a radiator shop nearby that can repair and pressure test the heater core? They can tell you what it will cost for 10 minutes of labor.
Third, do you care about maintaining stock appearance? Chevy Duty sells a replacement heater unit that's easy to install and works great, but it's a small black cube and not much to look at. Have you looked in the
Swap Meet yet?
