I wanted to pass this on. I have had my 5D MKII since early Jan 09. I have not had to clean it once and it has been used extensively and mostly outdoors. Overall a good success to Canon's internal cleaning since on all my other Canon's I would have long since had to open and clean.
However I finally got a large piece of something, blown in during a lens change. It was large enough to see on the LCD with very little magnification.
The camera couldn't clean it off, so I figured I would use my normal method on this type of item, which is to use a visible dust brush, full frame size and make two quick swipes. This took care of the large piece of trash, but on the next day's shoot, I started to notice 3 large smudges off to the upper left. The lines were soft so I assumed they were not a scratch.
When I got home I open the camera and on close inspection with a good magnification I could make out the same marks on the sensor. I had to use 3 standard sensor swabs with Eclispe (1) to get the marks off. I can only assume that they were oil that the brush picked up when I made the first cleaning. I somehow got the material on the sensor. I have to assume that I allowed the brush ends to get under the edge and some lube oil got on them.
I had this issue on my 1ds MKI, but never the 1ds MKIIwhich now has over 120K exposures on it. It has plently of other dust issues, mainly in the corners.
Just wanted to let others know to watch the brush if you are using the Artic Butterfly style brush, i.e. dry brush, on the sensor of a 5D MKII, don't let the brush get under the edges.
Paul Caldwell Photos of Arkansas