Manual focus problem A700

[silverman166]

As a bird watcher, many instances require the use of manual focus. It has performed perfectly since new, but now I find I cannot get a good focus through the viewfinder manually. I've compared photos taken with AF and the best I can do manually, and manual results are disappointingly slightly off. It's not lens specific, I've cleaned the viewfinder (and my specs!), all to no avail, so I assume something has changed internally with the camera.

Any suggestions, please - and I don't want to change my camera!!

Thanks.