I had a little accident with my 70-200 2.8 is II lens. Simply fell out from backpack (height about 10cm, really nothing I thought) and the alloy mount hit the floor. I shot a few pics - everything was fine.
Couple days later lens produced errors with the body. Polish Canon service replaced the appreture and fixed the problem. However, after the lens returned home it prooved not to be sharp any more. No AF adjustments could solve anything, because the sharpest pictures (focused manually on Liveview with 10x zoom) were still soft.
I sent the lens back to the service, included the test shots with descriptions, as well as my body (canon 7D) to be sure they check they work together. After two weeks got the lens back with the suggestion, that they could replace USM, because it sounds like it "perhaps soon could be broken" (noisy to them - completely silent to me and other guys I asked). But otherwise the lens is optically perfect.
The results are shown on these crops (comparing to two other 2.8 lenses I have, of which this one was similar, if not the best, regarding sharpeness):
(different focal lengths, so different camera positions to fill the frame exactly the same. Crops from the center of the frame. All pictures f/2.8, on a tripod, mirror locked, remote release)
I am actually looking for other repair service (preferably in Europe because of shipping costs) capable of saving my lens... Polish Canon service e-csi.pl proved to be the opposite...
Any tips and recommendations are extremely welcome!
Best regards, from Poland