I had this problem and found the solution on Dieselpower`s blog, thanks dieselpower!, on the same blog there was a link to this community so here I am, just registered!

I had my D90 flash wrecked in a trip to the Grand Canyon (AR, USA) and for a full year just used 1" of ductape to keep it in place, Nikon service here in Chile charged me US$ 240 for taking a look at it plus any spare parts, no way!!!

I tried the Allen key first and fixed it, but as I ended with a small gap that would sure cause the flash to open when getting the camera into the bag I became ambitious and gave it a second chance...bad call, could not make it work again so I had to try the second choice: opening the flash, my comments:

- When you turn the Allen key it doesen´t matter if you do more than one turn, it will not brake as it only moves the catch (its a cylinder) without screwing or unscrewing, one turn will leave you just were you started.
- As said before, DONT touch the cables inside, they give a very trong shock (personal experience )
- Removing the catch and knowing what to do is very easy once you see it, no problem at all
- The catch is a cylinder with the top side (where the plastic clip rest and holds the flash closed) cutted in an incline, thus turning it will give you more or less clearance for the clip to click in place.
- Cutting will make the thinner side even thinner for the clip to click in place.

Hope it helps, it realy helped my camera and my finances

regards