A few months ago I asked for help with my 28-135 lemon lens. It had been fixed three times by Canon, but the problem reappeared each time. I spoke with the Canon Customer Service and they only offered to keep repairing it indefinitely. I sent an e-mail explaining the situation and asked them to escalate the issue past the service people. To cut the long story short, Canon sent me a brand new 28-135 lens with a 1 year warranty, and pre-paid for the return of the faulty lens. I just wanted to share the story hoping it may help someone in the future.