As suggested, pics of the lens with a light shining through. I see some specs and I added the fingerprint as I removed the lens. Is this enough to cause reduced contrast? I wouldn't think so but then I'm no optics expert either. I'm using pretty old XTOL so perhaps that could be the issue.
From the front:
IMG_2254.jpg IMG_2252.jpg IMG_2251.jpg
From the rear:
A few of the body:
IMG_2244.jpg IMG_2245.jpg IMG_2246.jpg