I've had more than a few, both Renix and later models, that leaked where the eaduator cross fins mount to the end tank or where the cross fin endplate mounts to the end tank. Hard to see in there, either the shroud blocks your view or other stuff from the front. Wrapping a piece of white paper towel around the end of a chopstick and poking it in a suspect area can tell you how high the leak is, a good flashlight can help. The coolant color stain shows up well on a piece of white paper towel. I have a blacklight flashlight that makes the coolant glow with some brands of antifreeze, which makes chasing down a leak a lot easier.
As the leak or seep releases pressure the leak slows down, but at the same time lowers the boiling point of your coolant.