Hi DWBOX2000, I was at the USCG station in Scituate back in the early 80s. Nice little town then.
I tried to save a little money buying a water pump a year ago and bought one on Amazon. It stated that it had a plastic impeller, but when it arrived it was metal. I installed it anyway, but plan to replace it early. As all have stated: buy Pierburg/OEM with the plastic impeller.
Here's a few good threads:
Jake Raby's advice:
Water Pump - Page 2 - Rennlist Discussion Forums
Discussion of aftermarket with early failures:
http://986forum.com/forums/general-discussions/55937-aftermarket-waterpump.html
A long discussion good points on both sides:
http://986forum.com/forums/performance-technical-chat/43533-geba-pump-metal-impeller.html