If that was my lens it would drive me crazy. Would I spend the money to send it back to canon, no. My 17-55 IS lens sucked in dirt but not quite as much as yours but close. First time I had my lens cleaned by Canon and the next two times I did it myself before I ditched it for the 16-35mm II. Read online how to do the cleaning myself and it was not that tough. How I did it on my lens was to carefully pry up the black ring on the front of the lens where you see the lettering "CANON ZOOM.....1:4-5.6 IS USM.....67mm". Get a small precision screwdriver or exacto knife and work it up. It comes up with a little pressure. Under this sticker are two or 3 screws that hold on a plate that secures the front element to the lens. Pull out element or turn lens upside down as you hold a cloth in your hand and catch it. Then clean underneath it and then clean the lens itself with a proper lint free lens cloth or blower. Put it back together the way it came apart. That is what canon does so why not do it yourself if the 17-85 is like the 17-55. I went the extra steps and made sure to make note of which specific screw went where and then made note of the position of the plate so that it would go back exactly the same. These details most likely won't matter but it couldn't hurt. Additional side note if you do the cleaning replace the black circular ring/sticker which has the lens identification lettering on it back into its position and only run your finger around it's surface to make it re-stick. It is thin, flexible and will get creased/indented if you use anything else to push it down.


I found a youtube vid to assist you http://www.youtube.com/watch?v=z8-nEjfZ-KE. Its a no brainer especially if its out of warranty. Probably 60 bucks with shipping for a cleaning at Canon.