A friend's son here at work has a 2008 Lincoln MKZ with a 3.L Duratec 3.5 V6 engine with 100k miles and the water pump has failed. How did he know? Water was found in the OIL at oil change. Ford put the water pump internal to the engine so when the shaft seal fails, water enters the oil pan. He was quoted $2k to replace the water pump or $7k for a new engine if they find damage caused by the oil. He's gonna tackle it himself for a few hundred $ and a **** load of time and effort and see what happens.