The replacement part is around £12 from a Porsche dealer and slightly more from Ebay. I've added a video to YouTube showing the layout of the inside of the door lock mechanism but the steps needed are fairly straightforward.
- Remove door card
- Remove window regulator mechanism leaving one bolt to pivot
- Drop window glass to give access to guide rail
- Remove window guide rail to give access to rear of the door handle
- Identify which part of lock has failed
- Remove door handle using single screw on edge of door frame
Once you have the parts removed it's a fairly easy process to remove the door handle and fit the new ball joint mechanism or refit a loose part that has become detached. It might sound like seriously involved job to remove the door mechanism and window but it's actually reasonably quick to do and reassemble once you've seen how it works. I've done it and refitted in the space of around 2 hours.