This right here! There’s a steel fitting in that brass. Now, brass in aluminum isn’t going to cause any issues, as the thermal expansion rate is almost the same. But that iron is going to expand a lot slower than that brass 90 will. So your puddle of coolant is most likely coming from an intermittent stream out of that joint. Put a brass nipple in place of the steel and you shouldn’t see any more coolant there, provided the intake flanges are good and true and a high quality gasket is being used.