Under the hood, the plastic "quick connect" fittings where the heater hoses connect onto the heater core will rot from the inside out. When rotten, they become very weak and may allow the coolant to seap out when the engine is warm and coolant system is under pressure.
Also, if you look on the passenger side of the water pump, you will see two smaller hoses coming off the water pump. Of these two hoses, the forward one comes off the pump, enters a "Y" pipe and splits up into two hoses. The Y pipe is made of plastic as well and will rot out over time.
The "Quick Connect" fittings mounted on the heater core. The fitting on the left is new, the fitting on the right is broken and old. They are both supposed to look like the one on the left. The heater hoses clamp onto these fittings.
And here is a picture of a water pump. If you look closely at the left side edge of the picture, you can get a partial view of the Y pipe.....they get rotten over time.