Strange ????

I've got a minor leak from the roof-light in our 2007 Nuevo.  When I got up to inspect it I found a, strange issue - there are loads of dried dead flies inside the sealed unit! Anyone any ideas how they could get there? 

Is that a small circular breathing hole I have circled in red?

No, I think it's just a drop of water.

Bet that's the vent hole for the double glazed unit. Should have a clear plastic bung in it, it hasn't hence the flies....imho.
A small bent pipe attached to a powerful vacuum cleaner and considerable patience may get them out, then put a bung in or at least tape over the hole (s)

Exactly right, IanH. I had exactly that in a 1981 Eriba Puck I recently renovated. If you are not eating your dinner or about to retire to bed, you can watch a youtube of a female fly giving birth to thousands of maggots, really squirting them out. All they do is hatch into flies and buzz around inside the double glazing until they expire. I got mine out with  vacuum cleaner with progressively smaller tubes attached, and from memory I drilled a slightly larger hole which wasn't noticeable after I was finished.

if you get a pipe cleaner made with a steel core rather than a plastic one , cut it to about an inch and a half , bend to a vee and put through the hole , using a magnet you can scrape the flies towards the hole and then suck them out with a vacuum.