Didn't know it used a O-ring, Learned something new !
This happened to me on a new unit from Advanced auto (few months old,few thousand miles) Got a replacement And no failures yet,it's been close to a year now !
Apologies, I will always assume we are shit talking the OEM radiator unless otherwise noted. That said, maybe better to refer to it as a round gasket in case someone wants to get technical.
