Jack the front end up on that side and shake the wheel by pushing back and forth on the top of the tire. Every upper loose and bad ball joint I've had would move back and forth quite a bit. I've never had a lower one go bad but I suspect it could be checked in a similar manner. And you know, the upper ball joint is part of the upper control arm assembly. If you have to replace it buy the cheapest one you find, they're all made by TRW in Canada and are the same unless there are some really cheap ones coming out of the far east now which I would avoid if possible.