Originally Posted by
Al1943
Try putting the wheel in backwards. If the wheel becomes off-centered the other way it means that the wheel needs to be re-dished. This is a fairly simple procedure and is done by adjusting the spoke tension to center the rim.
It you have horizontal dropouts, couldn't tell from the picture, the axle needs to be adjusted in the dropouts. I'm surprised that the mechanic didn't explain these things to you.
The bike mechanic who looked at the bike is one of the best and well established Bianchi dealers in my area. He measured the frame and checked the dish. I was a little surprised that he had no answer to why the wheel was not centered. I assumed, as you suggest, that the axle could be moved over to center the wheel. But, I have to trust the old mechanic if he says that's not the solution.