To clear up a point of confusion: The LEDs (Light Emitting Diodes) in an F3 are the one on the front of the body that indicates that the self-timer is in use, and the one in the viewfinder that indicates that a compatible flash's readylight is illuminated. AFAIK, the LEDs have nearly infinite lives, or at least they'll outlast the mechanical portions of the camera.
.
The shutter speed and metering info in the viewfinder is displayed on an LCD (Liquid Crystal Display), and this is the device that has a theoretically limited lifetime. It can eventually lose contrast and become unreadable. I assume this is the device you're talking about replacing. I think most of them will live far longer than 7 years.
.
The LCD is illuminated by a tiny incandescent light bulb that's controlled by that darn red button that almost never works right. Theoretically, the incandescent bulb might eventually burn out, but since the red button never works, it seems unlikely that bulb could ever see enough use to actually burn out in practice. Who would know, anyway?
