Nissan Micra Profile engine cooling system

Hi, I won't pretend to be knowledgable about cars so please forgive any naiveté on my part.
We have a 1999 3D Micra Profile. It has a slow leak in the engine cooling system that means the radiator needs constant topping up. Our local garage says we need to replace an aged pipe that runs under the engine. My wife has tried to locate this part at breakers and parts suppliers but has come up against not really knowing the name of the part required. Can someone help by providing us with a possible list of the parts in the cooling system or a diagram? I have searched online and retrieved a few pic's but don't feel very confident that I have the correct ones. All help and advice gratefully received.
 
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