Thought I would mention my experience with a radiator leak at the seal between the plastic end tank and the aluminum core assembly.
I had a small leak in this area for some time on our 1997 Ford Escort wagon. I
t only seemed to leak during a temperature transition, typically when I stopped and the cooling system cooled down and the pressure was relieved… Then there would be a few drips that would escape.
On long trips, it didn’t seem to loose coolant. I only had to add coolant every month or two to the overflow reservoir, the radiator stayed topped off as long as there was coolant in the reservoir.
Purchased a replacement radiator from a local parts store. Removed the old radiator and was about to install the new radiator, but I noticed that the overall quality of the new replacement radiator didn’t seem nearly as good as the original, 20 year old radiator. Decided to try to fix the leaks in the original radiator by slightly re-crimping the retention fingers all the way around both plastic tank flanges. Used a set of smooth jaw knipex parallel jaw pliers. Only crimped each finger a TINY bit, maybe only 10 - 25 thousandsth of an inch.
Because I used the car in an 'away from home ’ situation, and needed it to be reliable, I performed a pressure test on the radiator afterwards…
Plugged both hose connections with a combination of plastic cap and old radiator hose. Installed Schrader valve in one plastic cap to add pressure. Pressurized to around 15 psi with air, used a spray bottle of soapy water to look for leaks.
No leaks found! This was at least 4-5 years ago and it hasn’t leaked or required coolant since!
The rubber seals had likely taken a ‘set’ thus loosing the compressive force that maintains a seal… A small amount of re-crimping did the trick for me, maybe it will help someone else.