...until I come home after work last week and said daughter complains that her top box hinges have all broken but proudly announces that she managed to find the allen keys in my garage and has put the box on my workbench to fix. Thanks - so much for me working on the GT this week.
A quick visual inspection showed that although the damage was limited to the top of the box she had managed to snap off one hinge block completely and split the other three, hence completely seperating the top from the bottom. Because of the design of the lid there was no way that I could repair the broken hinge blocks so my only options were to either buy & paint a new lid or make a replacement hinge. In the end I decided to make new hinges, mainly because it was a challenge but also because we had used all the holographic paint in the course of the build and another 1/4 litre tin would cost the best part of £500. Now there's incentive!
Im sure that there are many ways to do this, but I decided to mill new hinges out of billet aluminum, which I admit is a bit beyond the average DIYer but nevertheless I thought it may encourage someone else to have a go at a similar repair themselves with more conventional techniques or equipment. This is how I did it:

First job was to cut off the broken hinge blocks with a Dremel & dress up the edge with a file

The material for the hinges was 2" x 3/8" aluminium bar. First job is to square the end of the bar.

After drilling the 3.5mm diameter through holes, I then rebated the lower half so that the boss of the hinge would overlap the edge of the lid.

Milling the gap between the two hinge blocks.

Had to file slots into the lip of the bottom section to clear the hinges. I tried to think of a better way to make the hinge to avoid this but found that this was the only way to have a hidden repair.

I dummy assembled the hinges onto the bottom, dropped on the lid and then free-hand drilled screw holes through the back of the lid & spot drilled the hinges. I removed the hinges & tapped them out M4.

This is how the hinges fitted on the inside of the top section. I had to taper mill the rebates to match the profile of the lip & glued them into place with high strength epoxy.

Temporary pan head screws held the hinges in place whilst the epoxy set.

Final job was to countersink the lid, cut the posi screws to length & fit them one at a time. I also reduced the knurling at the end of the hinge pins to make them an easier fit in the non-compliant aluminium. Job done.