I wonder if radiator shops clean and repair/renew old stock heater cores? After all, the heater core is just a mini-radiator isn't it? I would hate to have to purchase a Chinese replacement.
Most shops wont touch them, you can buy replacement for 1/2 the cost of repair-I just went through it. Now I am going through it with my radiatorrotest:
Even in the 70's when I was "in a previous life" and sold auto parts, it was not common to "rebuild" heater cores IF THEY were available as a replacement.
Of course, back then, you could actually buy them, LOL