Could the green goo possibly be leak detecting dye put into the A/C system? Or maybe A/C oil? The A/C system really has no way of mixing with antifreeze - there's no interface at all between the cooling and A/C - unless you have both a leak in the cooling system, and a leak in the A/C tubing in exactly the same place (highly unlikely - and you'd notice the cooling leak).

Troy
1995 E420