Past 2 days, no leaks. It seems to only leak when it is very very cold at night. It warms up here to 50s and 60s, but at night can get to 20s and below. If I recall correctly the days it leaked it was below 20 at night.

I am guessing/assuming that there is a very small leak hidden behind the plastic sides, when it warms up the metal expands and it doesn't leak (since there is no smell nor leak when running and it only leaks late at night) and when it gets cold as a well digger's behind the seepage occurs. I know that isn't scientific since the leak should occur as soon as the radiator cools off, but it doesn't seem to be.

I've even run it hard during the day to try to force the leak.

Guess I'll be buying a new radiator for peace of mind.