Upload & Sell: Off
I decided to risk shipping it to Canon. The lens was received at Canon on 12/9, repaired, and received back here on 12/15. That was excellent turnaround for an ordinary consumer like me.
"Your product has been examined and it was found that the part was loose, the screw was loose. The part was replaced. Product functions were confirmed. Adjusted center tilt/front/back focus and cleaned factory specs.
Parts: Rubber Mount and Lens Mount Assembly (Type 2)"