Parasitic drain on battery.

[Jamesp]

I did chase down a similar problem on a 72 Duster where we still had a leak with all the fuses pulled. In that case we were able to pull a firewall multiple connector and go pin to pin finding out it was a "seatbelt interconnect" box buried in the dash. We disconnected it and the leak stopped. Everything still worked on the car and we never did figure out what that box did other than draining the battery. I don't know where the harness production break is in the Boxster but I imagine there is one somewhere.