This seems to be a common problem with the Timing chain cover. The chain can eat away at the cover, then punchures/grides a hole in the water line/pump area leading to your problem. Do a search and you'll find a lot of info. Look inside the timing chain cover for a chain width area where the chain would of grinded away at the cover. Might also replace the chain guides with metal ones. I'll even bet that you found broken plastic pieces on the bottom of the oil pan from the previous chain guide.

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Hope this helps