My D300 is focusing behind the subject during critical focus situations. Fine focus tuning does not fix it. It is not a mirror or focus screen issue, because manual focusing with my eyes works just fine. The focus confirmation is off also, and seems to match the AF error of focusing behind the subject. If I stop down enough, I can get the subject in acceptable focus, but I am not okay with that limitation.
The factory service manual is available for free download at https://learncamerarepair.com/downloads/pdf/Nikon-D300-service-manual.pdf
There are some manual adjustments for focusing then on page 58 there is the instructions for the Inspection and Adjustment software. I do not know where to get the software. You may have to take it to a Nikon authorized repair shop to get it adjusted.
Thanks Ced. I have adjusted the fine tuning, but it was insufficient. I may have to stick with smaller apertures on this camera. It has always had more difficulty than it should focusing in challenging light, so it may be the af module...