I have used Autozone Water Pumps on other Vehicles with no early failure issues. It is hard to say if that transistions over to Mercedes.

I think there is also Driver issues when it comes to overheating a Car. Some Drivers don't feel they are only responsible for turning the Car on and driving it in a resonably safe manner. They don't take any responsibility for looking at gauges and listening and smelling what is going on with their Cars and drive them to death when there is a problem. A life time warranty is of no good to those types.
With the above type of person you are better off getting the best parts avaliable.

The above described situation is a sore spot with Me as My Wife continued to drive My Van and did not know She overheated it due to never looking at Gauges and thinking the Coolant Smell was Gasoline; overheating caused by a small Water Pump leak. She also never told Me the Engine was knocking. I did not find out till I drove it Myself.

And, yes it spun a Rod Bearing and ruined the Crankshaft. I have not overhauled an Engine for 23 Years and am extremely unhappy to have to do it now.

Back on subject. The assumption is that the higher quality Water Pump is going to last longer and not give someone the chance of destroying their Engine for a longer period of time then the cheapie one. So you need to ask the Car Owner what they want.

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84 300D, 82 Volvo 244Gl Diesel