Yes, I agree fully with Richard.....what I meant to say was that if you have fully exhausted your options with Canon service without satisfactory resolution.....and before you buy a new cam.....then and only then try a wet clean.  In other words...as a LAST resort!

Also be very careful with using any type of cleaning fluid.....and make sure you are using the RIGHT type of fluid.   There have been problems with using older fluid formulations on some of the newer sensor filters....be aware!

Regardless, something just doesn't sound right with this situation....Canon SHOULD be able to clean the filter if it is a dust or oil problem....or, as Richard says to remove the filter and clean....they do this ALL the time!   I think there must be more to the story....and you really need to press Canon to get to the bottom of this!

Good Luck!

In youth, we learn....with age, we understand.