Not the one I want LOL, the "free" Sigma 70-300 I just got will not AF and likely is junk, but it is filthy dirty inside on at least one element. In my search I found this: I have at least a couple of Canon lenses and a 7D so this might be useful....
https://www.youtube.com/c/CamerasLensesEtc/videos
https://www.youtube.com/c/CamerasLensesEtc/videos
