I agree, it could be lots of things. start by pushing, pulling and prying on every thing you can find back there, then take that wheel and put it up front. if its the wheel the wobble should shift and you should feel in the steering wheel... supposed to rotate your tires every oil change or so any way
I know someone with the in-hub removal tool, so its fairly quick for him. Otherwise they remove the hub. But, its not technically hard to do with the correct tools.