[KevinH1990]

I think you are correct. Here's what Tool Pants told me on RennTech:

There might be an error with the Walker application guide catalog, where you look up Walker part number by the vehicle. In this Walker catalog 250-24423 is shown for the rear sensor for a 2000 Porsche Boxster. If this is a Walker error then it will be repeated by oxygensensors.com

PET has the rear sensor as Porsche part number 986-606-128-01. Using the porsche part number on the Walker oem parts interchange catalog the rear sensor comes back as a Walker 250-24647. The front sensor also comes back to the same 250-24647 number.

I think you need 250-24647 and the 250-24423 is a Walker catalog listing error that got repeated by oxygensensors.com.