I am in the process of installing a new heater core (see this thread). I test flowed the new heater core with some water and it didn't leak. However, after putting it into the box I noticed a small crack (see attached pictures) where one of the pipes is connected (welded?) to the core. I don't know if this was there before I installed it, or if it occurred during installation. I'm worried that under pressure this joint will leak. Should I try and return this heater core for a replacement?