SD card snapped off in expansion port
The SD card had snapped off in the expansion port and could not be removed which entailed fitting a new port.
I also used YouTube videos to explain how to dismantle the GoPro and the whole thing went very well. Anyone attempting this should only need reasonable DIY skills and the confidence to do it. Be careful with the removal of the front cover as I broke it just above the lens where it is most flimsy. I put a tiny spot of super glue on it while I got on with the rest of the job and by the time I came to refit it, it was good as new. Unfortunately I didn't think to take photos of the work in progress.
You may need to use a magnifying glass. I have one on a stand it it was particularly useful.