When I got my 25-50, it was immaculate on the outside. Not a scratch or dent, nothing. But images were so soft they were fuzzy. The inside was filled with dust, maybe some fungus. Not sure. I sent it off to have it cleaned. When it came back, it was as pretty on the inside as it was on the outside, but the lens was not reassembled properly. It all works and feels fantastic, except the aperture ring is not properly indexed. In order to get properly exposed pictures out of it, I have to put the compensation at +2. It works, but it's annoying, and I need to find someone to index it right.
What I like best about it, is I can't find any color fringing, which gives images a clean look. I also appreciate its relatively low distortion. It seems to have less distortion than most modern primes.