Nikon F100 Diopter Problem

Question

I have a problem focusing through the viewfinder. Everything was fine until one day I twisted the diopter adjustment (just to test it's effect) with a heavy hand and I think whatever it adjusts has come off its rails as there is now something loose in the eye-piece. I can get it in focus with a shake but if I point the camera up something moves and if goes back out of focus.
If I get the correct screwdrivers do you think it would be an easy fix?

Regards,

Adam