After over two years of flawless functioning, my Canon A80 has developed an odd defect. A small, round, dark smudge appears in the upper left of every photo. It's not real obvious, but noticeable enough to be annoying. It's most visible when that part of the photo is a uniform color (i.e. blue sky or grey cloud cover). When that area of the photo isn't a uniform color (i.e. foliage), the smudge is virtually invisible. I've seen one other reference to this, on a new Canon A710IS, but mine appeared after well over 1000 photos. Any ideas on what it could be? Sensor going bad? Dust somewhere on the innards of the lens? (It's not dust on the outside of the lens.) Or if there's any way of fixing it?