Just found a guy on YouTube replacing the actuator. Search "Boxster fuel filler flap" and you will find him with a white Boxster just like mine. Tried to find the URL but couldn't.
The video is a bit dry and it takes a while to get used to the camera angles, but really useful. You see him towards the end of the video, separating the arm from the old actuator and fitting it to the new one. I think mine has just fallen off. I might use a bit of silica to help them hold together when I refit it to hopefully stop it happening again, but still allow me to remove the arm if I need to in the future. Don't know how it has happened, I literally just touched the wire and it fell off in my hand. That's my story and I'm sticking to it.
The car is full of fuel and the flap is not jammed so the only problem is the filler cap is not locked. Can't remember the last time I heard of a car being syphoned and its kept in the garage anyway. The spring holding it shut seems to be fairly strong so don't expect it to open when driving.
Anyway looks a fiddly but quick job and cost free hopefully. I will get round to it when I next need to remove the wheel.
Update to this since I could find no reference to it anywhere for a 987.2.
The wheel liner is in two parts and only the rear needs to come off rather than in the video where the whole thing comes out. I couldn't get it to sit back in the arch neatly at the first attempt. It seems to not want to sit nicely around the inside of the arch, as if it was an inch longer then when it came out. Left it in the sun for a bit and on the second try it just fell snuggly into the wheel arch.
The Evap Cell is held in by a single bolt, rather than the 2 in the video, and then is pulled outwards from 2 rubber locating lugs on the back. Put a bit of washing up liquid on them when reinstalling it will make it much easier and saves 20mins of harsh language. Nothing else needs to be disconnected it will just hang out of the way while you reach into the top of the wing.
The actuator comes out exactly as the video shows. Very fiddly, but a T20 Torx taped into a ratchet spanner makes it possible.
The rod snapped back onto the actuator and appeared to be secure without the need for silicon.
About an 90mins. Less if I had put the washing up liquid on straight away. Hope this helps someone in the future.
