I had fun removing the scuttle on mine today. The lip of the scuttle which fits in the groove below the windscreen is barbed.
One half came away ok, the other started to break leaving the lip in the groove but I got that out with a butter knife which started the rest.
To note (somewhere), below the scuttle just drains through a gap into the wheel arch so nothing there that particularly needs cleaning out.
I had several inches of leaves and dirt stacked up behind the wheel arch liner. So well worth getting in there to stop rust.
I believe my leak was from the sunroof. I palled the passenger side roof lining down, very wet within, and the rodded from there. The pipe comes out by the hinges as shown. I used a syringe to push water through and lots of dirt came out and now everything runs free.