The bit that opens the flap is part of the hinge and is just a piece
of plastic that goes up against the bodywork at the hinge and bends
slightly. Then when the release is pulled it "unbends" and opens the
flap. It breaks if you close the flap too hard. To fix it you need a
new flap, and it comes unpainted. However I have got round this.
Gently tap the long hinge pin upward about an inch so that the smaller
diameter parts of the pin are in-line with the two parts of the hinge.
(you'll see what I mean when you do it!) You'll see a bit of plastic
protruding from the flap just above the pin, which prevents the pin
from working its way upward by itself. Then pull the flap off the pin.
With a sharp knife cut around the join of the painted bit to the rest
of the flap until the two parts come apart. Do the same with the new
flap. Clean up where the two parts meet and super glue the painted bit
to the new flap part carefully so that no glue gets on the painted
bit. Put a weight (book?) on it and leave for 30 mins or so. Then push
it back on the pin and tap the pin down so that it is under the
protruding bit of plastic.
All should now work!