Multiple misfires 1,2and 3

[Gelbster]

Unless the other O2 sensors have been replaced ,it is prudent to replace all at the same time.
Make sure you get the correct part number - your Boxster uses different O2 Sensor to later M96.The Pelican Parts Catalog is correct.
While you are in there, check the coils for cracks(Search), oil in the spark plug tubes, old plugs and vacuum leaks.All potential/likely sources of misfire codes.