The oil fill pipe on the Porsche 996 engine has a tendency to crack and break after 20 years. It will cause the engine to run poorly since it is a sealed system. Replacement is not too terribly difficult. We made this video at BreitWerks so you can see what is involved in the process or maybe it will help you if you work on your own 911 Porsche.
Idk, I replaced mine without removing the throttle body and plenum. Good video though
Looks like you know what you're doing, when I need mine replaced you're the man.