Last year I took a virtually new 24-70L to Canon in Irvine, California, to be electronically recalibrated because it was back-focusing. I was assured by Canon that the lens would not be dismantled. However, when I returned to pickup the lens, I was told that three collars were replaced (on a brand news lens, go figure). I was upset because I had specifically instructed the service center to not open the lens because it was new and I was going to return it if it could not be electronically recalibrated. Also, after the "service" the barrel was slightly loose and the focusing inconsistent, so I called and complained to Canon corporate in NY. A really nice lady at Canon confirmed that my request was not honored and authorized a free replacement lens, which I received and was very pleased with because the AF is accurate on the new lens.