If it is the pump.
http://www.986forum.com/forums/showthread.php?t=16490&page=2&pp=20&highlight=impeller
Went to a cooling tech session at an independent shop last year and Bob the owner said he sees a lot of these at around 60,000 miles.
Marvin who also has an independent shop has replaced 2 this week.
As far as buying a replacement that is the same as what just failed. Why? Crappy oem pump as far as I'm concerned. I have a 1988 Toyota truck with 156,000 miles with the original pump. Porsche also sells a crappy plastic coolant tank made by Geiger. I say go aftermarket. $110 on ebay or your local parts place like Kragen.
Marvin has a press. Last week I asked him to press off the pulley to see who makes the pump. As soon as the press started pressing on the shaft the pump broke. I want to see behind the pulley to determine who makes the pump.