Not to question your knowledge or experience guys, but make sure you re-fill the coolant properly. Too often people don't, and then come back in with problems again. Also, the petcock on that radiator takes a little work to get snug. So if you have a very minor leak at operating temps from the petcock, it just isn't quite tight enough. If it's really tight when cold, let it warm up a little and tighten it a little more, and it should seal. I just wrap my arm in a towel/rag/dead animal, and reach down there and tighten it up. You might even put a little teflon tape on it, just keep it tidy.