er..i have the same problem with that but not toyota.
just like what u have gone through, alignment, tones of servicing, but still keep coming back. mine was serious, turning to left side and i have less right angle for turning which means U turn on right will be hard.
this goes on for 3 years and just last month, my front tyres worn out, sent to tyre shop for new tyres and alignment, and done. the problem never come back again. I was wondering how on earth the so called "official" servicing team could not get it to work for the pass 3 years.

hope u can figure it out.