Just thought I'd add an update. At the gentle urging of a friend here on the forum (thanks David!), I bit my lip and called Canon service and initiated the warranty repair. Within a few hours I had the email with the shipping label. I boxed my camera up, attached the label -- UPS Ground -- and shipped it off. This was Tuesday last week, and I confirmed delivery to Canon on Monday morning of this week, California to Virginia. Canon did the repairs and shipped the camera back to me on Wednesday via 2-Day FedEx, an interesting combination of shipments I thought... Anyway, it arrived today and according to the sheet, the AF work was done AND the firmware was updated. That part is really interesting, because I had already installed the latest firmware update(
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Whatever, the result is the camera focuses immensely better, locks on moving targets and stays locked on. It may be just my inner glee being overly stimulated, but it really seems even the single-point, single mode AF is much more accurate.
So, +1 happy camper!