Just an update -- I sent the camera to Nikon (Melville), and they fixed the AF module (don't know if they replaced or recalibrated). Anyway, it's working fine now after an initial scare. They changed the diopter setting, so when I took the first few shots, nothing would focus through the viewfinder, but the shots looked to be in focus on the LCD screen. Then I remembered they always reset my diopter settings. Doh! All is now good.