Tell u all the truth, I could sense that they were nervous on this issue. It might be a manufacturing problem. I don't think Canon service center Singapore can do much other than sending my lens to factory for recalibration. In that case, I prefer to receiving a new replacement. It's not my fault to buy a back-focused lens. Canon should do an investigation in this case to evaluate the policy regarding calibrating/replacing back-focused 24-70L.