Well, it won't be any 1 thing that may be worn. Just go through and see if anything has excess wear that you can replace. Mine doesn't wobble that much, but it's an older pre-x savage. I'm running lunsfords turnbuckles for steering, so the balls/cups are larger than stock and wear less quick.
With all the connections between the servo and the wheels, there's bound to be some slop. Some of which can be minimized with shims, like in the c-hub/axle carrier area. Also, the bearings or bushings in your steering post uprights may be worn. Any/all ball cups get slop over time.
The larger the tire you run, the quicker slop will show up. Especially if you run in wet conditions that get water in the tires that throw them out of balance or if they are just glued out of balance. All that high speed running with tires out of balance really punishes all the pivot points in the suspension/steering.