New one arrived last night. Haven't tried it yet. But something just occurred to me: I never checked the Amazon copy's firmware.
I'll be methodical and realistic with #3, also from Amazon, AlanF! I'll be using the test targets you shared some time back first, then a SpyderLensCal. Looks like indoors with all the rain we keep getting, but on a tripod and with good lights. If in the unlikely event I have a lemon and it has to go back, I'll keep it to myself. So if you don't see I've posted new bird photos within a week or so, and some happy thoughts about the 100-500mm, you can surmise--but not read any negativity.