For future reference, stubborn cotter pins can be dealt with fairly quickly--just break off the ends that are sticking through the castle nut using pliers, by bending back and forth. You just need to make enough clearance to get your socket on the nut, then just undo the nut with your impact wrench. It will shear off the rest of the cotter pin parts as the nut comes off, then you can remove the pieces in the middle if need be. (or if replacing the ball joint/tie rod end, you're ready to go)