Canon USA has issued a service notice for Canon EOS 1D Mark III and Canon EOS 1Ds Mark III owners.
Service Notice: EOS-1D Mark III/EOS-1Ds Mark III: Oil Spots on LPF Surface
Thank you for using Canon products.
We have discovered that images taken by some EOS-1D Mark III and EOS-1Ds Mark III digital SLR cameras may exhibit ring-shaped spots. We would like to convey the details and our service policy.
We offer our most sincere apologies to customers using these products who have been inconvenienced by this issue. Going forward, we will spare no effort in our quality management to make sure our customers can use our products with confidence. We hope our efforts will earn your understanding.
Phenomenon
Images taken may exhibit large ring-shaped spots.
Cause
These ring-shaped spots are the images of oil lubricant on the surface of the low pass filter (LPF), which is located in front of the CMOS sensor.
This oil is used inside the Mirror Box to lubricate some of the camera's moving parts. If the oil is applied too liberally when the camera is manufactured, it can become scattered onto the surface of the LPF through normal camera operation. 
* Image of Back Side of Main Mirror
The image above shows the top of the mirror box when the main mirror is flipped up. The white spots in the red circles are excess lubricant oil.
Affected Products
EOS-1D Mark III and EOS-1Ds Mark III digital SLR cameras
Support
We ask that customers who are encountering this phenomenon or, who have noticed that oil is visible on the surface of the back side of the mirror, please contact our Customer Support Center. To prevent oil from scattering, which may seriously affect images, our Customer Support Center will arrange free cleaning of the mirror box to affected customers to remove the excess oil.
Oil Lubricant Used in Cameras
Measures are being implemented to control the amount of lubricant applied during manufacture in order to reduce the occurrence of oil spots. However, because this lubricant is required to ensure proper operation of the camera's precision mechanical parts, it is impossible to eliminate all instances of oil scattering. If you require CMOS sensor cleaning, please contact our Customer Support Center.
Thank you for your patronage and support of Canon products.
This information is for residents of the United States and Puerto Rico only. If you do not reside in the USA or Puerto Rico, please contact the Canon Customer Support Center in your region.
Contact Information for Inquiries
Canon U.S.A., Inc. Customer Support Center
1-800-828-4040 (toll free)
Email: carecenter@cits.canon.com
Click here for support options and hours of operation.
I can tell you from experience that getting this oil cleaned off the sensor until it no longer continues to be splattered there (or transfered there from a sensor brush) can be extremely frustrating. I welcome the attention Canon is paying to this issue.
Posted
May 14 2009, 10:16 AM
by
Bryan Carnathan