I just bought a used Nikon F4. It appeared to be in pristine condition. When I first got it the numbers in the viewfinder lit up and it seemed to work fine. I noticed however that the prism does not latch on...it will slide off, as if the latch wasn't working. I noticed that the track on the prism itself appears rounded off, but the latch on the camera seems ok. During the first roll however, I noticed the viewfinder display numbers went away, and they would come back if you tapped on the prism. This applies to both the LCD displays and the backlights. Now the I can't get the LCD displays or the backlight to come on at all, except sometimes they do if you push down on the prism. The camera continues to operate when the displays aren't visible. Do you think this is due to the prism or the camera, or in other words, what are the chances that buying a new prism would fix it? Also, the camera operates even when the viewfinder numbers aren't there. Do you think it's working fine, even when the prism isn't displaying anything?