I'm dealign with htis very issue as we speak- My sensor arrived in absolutely filthy condition, and this was a brand new camera too- I shot with it that way for a year thinking it was just dust, avoiding light areas in my photos so I wouldn't have to work like a dog removign htem in post- I finally by accident found out abotu their product advisory about 3 weeks ago, and arranged for canon to fix the proble, and of course clean the sensor- They fixed it, but only cleaned the center of hte sensor as you will see in the following photo- look especially at the upper and lower corners- http://www.flickr.com/photos/55331349@N05/10348299754/#sizes/k/in/photostream/
I've enhanced the tonal contrast in the sky shot, but beleive me, even without enhancement, the spots are so prominent and so prevelent that tryign to fix the spots in post is a ngithmare- I sent Canon tech the link to the photo and let it be known that this was the very first shot after IU got it back from their tech service- now htey want me to send it in again- after beign without my camera for a week+ already=- Right during fall foliage season too!
I beleive the issue is bits of plastic from the wear and tear on the camera due to insufficient lubrication in the mirror box-
My camera is out of warrenty next month- so not sure how they are goign to keep fixing it- I had just sent in the camera two weeks ago, and they tried to make me pay for soem other repairs that were needed claimign it was 'out of warrenty' (I hadnb't sent in my warrenty card unfortunately-) but I was able to show that it was still under a year old, and the other issues were fixed (My portrait mode scroll wheel never woerkd right, and was gettign other issues liek 'caution 02' which was fixed by firmware update etc-)
I'm not very happy with htis situuation at all- I literally spent every last dime I had on this camera- was suepr excited to get a 'rugged' camera, thinking it would last a good long time- only to find out I may have gotten screwede by gettign an early model with mechanical issues that might cause premature breakdown
IF anyoen else is havign hte issues, please get with canon to fix the issues as them ore peopel that are havign the problem, the likelier canon is to make good on the issue- But perhaps they will put it off utnil people's mirror boxes begin actually failing due to mechanical failure- (which will likely happen AFTER the warrenty has run out- Hopefulyl htis issue can be resolved soon- but it doesn't look like it's goign to be- so those of us with hte early models are apparentyl crap out of luck-
The 1DX has huge promise, but the early models seem to be an issue at htis point
one more way to tell if you have early model is if the 6'th number from your left- countign left to right, on hte seriel number is a 0-7 I guess- but also look in battery compartment for either an A or a black mark on the silver knob just inside hte compartment