Chosen Solution
The waterproof(?) cover of the USB charging port has broken off. Can this be fixed/replaced without sending it in?
Yes you can replace this without sending it back for replacement. This part is held in place with one screw inside the battery cover by the USB port. Unscrew that and lift up the plastic that holds the cover in place, do the reverse to put it all back again.
replace it, you can buy the part on ebay for a few dollars.