<p>Thank you all for the comments. I would have thought the same, that fungus would unlikely cause mechanical problems but rather degradations of the lens coatings. The inner lenses are spotless after the fungus removal and there is no trace of spider-web like trails or anything like that. Also the aperture blades move smoothly and easily, and I've checked the lens mount for damage, but it looks almost new.<br>
Re live view, it's hard to tell on the relatively small screen and I would have said the problem does not show up there - however, I took a video with both my 50mm prime lens and the 17-55mm lens and there clearly is a blurriness across the whole picture in the latter. I would assume that video and live-view picture are the same in that regard?<br>
Taking a picture of a closer object also shows that this isn't a misaligned focus point, as there simply isn't any spot from near to far that's focussed.<br>
I guess there's no way to identify the real problem further - frustratingly the Nikon center didn't even pick up on the issue, so there goes my confidence in getting this fixed through them. I might look for an independent camera shop enthusiast that has some mechanical skills or the right instruments to diagnose this...not much to lose, is there.<br>
Again, thanks for your thoughts and if anyone does have any further suggestions to test this, please comment.</p>