I've owned about 20 Nikon bodies since 1980 and I've had winners and losers both new and used. The best looking used FM I ever bought - lightly used by an amateur - had a terminally defective shutter. Sold it for parts. My first F5, brand new in 1998, had a short that would run the batteries down within two hours. Nikon replaced it of course, but it was broken brand new out-of-the-box. An old brassy Nikkormat EL that was so worn it felt like the film advance lever would wobble off every time I advanced the film was deadly accurate and one of the most reliable cameras I have owned. I do think that the cameras that used accessory motor drives wore out quicker when used on the motors than if they were used manually.