I talked earlyer last week about my older sigma lens i bought off ebay and got burned on . Well everone told me it would be hard to take apart a lens and put it back together well today i dove in and did about three time and could not figure out what was wrong till i got a magnifying glass out and found this .Go here to see the gears.http://www.flickr.com/photos/hobosnob/5423409859/
The one on the right is the one that i need to replace. so now i'm going on the search up and down to find a new gear so my purchase was not such a waste. The auto focus gear was fine but the one it matched up to is the one on the right and one on the left is the one that matches up to the main gear that goes all the way around the lens which was fine to.

If you know of anywhere to get parts or have any ideas i'm game i think tomorrow i'm hitting the thrift stores and pawn shops to see if i can find a use lens that i think might have the same gears its worth a try.