My 4-matic suffered from quick tire wear, but it wasn't focused on any one tire. I would suspect alignment/balance/air pressure as all contributing issues on yours. With mine, I had a 4 wheel alignment done right after I put on new tires (4 of them), and there after had them rotated every 3000 miles or so. This helped tire life quite a bit. Problem is that I ended up paying almost as much for tire rotation and re-balancing as I paid for the tires to begin with. No escaping high tire maintenance on the 4-matics!