By chance I was talking to a mechanic today about the use of a plastic vs. metal impeller.
This mechanic works at a dealership so he has never seen a metal impeller pump on a Boxster, as that is not what Porsche uses or sells.
He did say that VW use to use a metal impeller and when the bearings failed the impeller would grind away at the aluminum engine case, and perhaps that is why Porsche uses plastic.
I like the idea of using quality aftermarket parts that cost less then what Porsche charges. I'll bet that ebay pump is aftermarket with a metal impeller. Take some pictures of it and your old pump. If the Porsche water pump was so great to begin with, then it would not have failed so soon. I say put it in.
This mechanic gave me a pump he had just replaced. You can see the plastic impeller broke when it hit the case when the shaft wobbled due to failed bearings.
As you can see a chunk of the impeller is missing. When I see your pictures I will tell you more.
He does not replace the thermostat or hoses unless there is a reason to do so.
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