Beware of the copper radiators with brass end tanks that only have 15 fins per inch instead of the 20 fins per inch your copper radiator has. That's a 25 percent reduction in cooling surface. They will not cool properly. I suspect if you look closely, you'll find the left composite end tank is leaking close to the bottom. If you can find a really good radiator shop, they could fabricate brass end tanks to solder on your radiator to replace the composite tanks. I've been lead to believe there are some aluminum radiators out there that will cool properly.
I'm only relating the mistake I made when I purchased one of the replacement copper/brass radiators. I ended up removing the end tanks from both radiators and soldering the new tanks on the old radiator.
Richard