I have a very well used 135 QC which doesn't have a large amount of contrast. If I have some time I'll clean it and see if removing some of the internal dust will make a difference.
That bit of dust doesn't interfere with anything, even scratches on the front element has to be huge and then the lens stopped way down to show up.
The rear element is always an issue but again I have a 105mm f2.5 with a small nick and I haven't seen any interference. I did buy a Tokina 17mm pro from B&H the lens was like new but the rear element had some sort of coating deteroration looked to be from use of the wrong cleaner along the lower edge. That showed up on the bottom corner of all my images. $120.00 17mm PRO Toki was to good to be true, I sent it back.
135mm f2.8 Nikkor QC I haven't messed with it much I shot a few photos with it so far and it's not a bad lens.
Just haven't had the time to evaluate it's limits.
I do mainly B&W so it's not a great way to evaluate it's color contrast. this was taken on a QC 135mm f2.8.