98 Toyota Avalon has steering issues. Steering wheel occasionally jitters when decelerating.?

We've owned a 98 Toyota Avalon 6 cyl auto for about a year. It only has about 117000 miles on it. It has 2 problems or maybe 1 combined problem. First, it leaks power steering fluid. The leak location is not known. The power steering fluid was allowed to get low. We have since added Lucas Stop Leak. We noticed it was low again and added a second bottle of stop leak. The second problem is that the steering wheel has started to occasionally jerk/jiggle or make short, quick pulls to the left. This has started happening since it's gotten colder and the jerking occurs frequently but not constantly when you take your foot off the gas. Can anyone tell us if this is a power steering issue or is the problem related to the drive axle, trans axle or CV joints?