Mine belongs to the early production unit with "0" in the 3rd digit of the serial number. It is supposed to have the portrait problem, and I could see there is very little loss of resolution in potrait mode at 300mm, viewed at 100%. To those people who own this lens, My questions are, 1. Did you notice an improvement in resolution at 300mm portrait mode, after it was serviced? 2. Did the problem returned after a couple of month of use after it was serviced? 3. Was the zoom creep fixed and then returned after a couple of months use, after it was returned? 4. Does anyone here on the same situation but never bothered to return the lens, and after months of use the lens sharpness at 300mm portrait mode worsened or stayed the same, compared to when it was new? I'm asking this because, If after months of use prior to the fix, and the barrel loosens up again, the small problem might return . so it might not be worth it, to send the lens after all. Thats what I like to know. Thank you for your time.