My F was serviced by Advanced Camera http://www.advancecamera.com/repair/
about a year ago, it was a camera I bought knowing that it needed service. Meter did not work and shutter speed were off.
When i picked up the camera I was in disbelief when I saw how good this camera could look. Meter is working and shutter speeds are right on the money.
As far as I remember Heidi Fisher is the Nikon guru there, she did wonders to mine and I highly recommend them.