The right rear tire on my 2000 Outback 5speed is almost worn to the indicators after only about 15000 km. The other three are fine, just normal wear. The wear is fairly even over the tire, no cupping or scalloping, as if the tire is either dragging slightly or trying to turn faster(!) than the others. Does anybody know of a probable cause?

Are you particually fond of turning left going uphill? That's how one of my tires wore out.