Sorry I didnt' reply sooner. I don't get notifications anymore from this site. I've had 3 struts replaced under warranty. This was when I was driving it a lot more than I do now. First time it was both rear struts. Then the second it was only the back left, or right. I don't remember. I'm finding now, that I'm experiencing the same sticking strut problem whenever I push the car a little bit. But I might drive it once a week now, so it just doesn't bother me enough to pay for a new strut now that I'm well out of my warranty. Try lubricating the shaft. I'm not sure exactly what type of lube to use, but give subaru a call and find out what they use. From what I remember, the strut issue I had stemmed from a lack of lubrication on one of the bushings.
Hey..I wonder if you had more than one problem with ur suspension on ur STI? Read my reply on the post of rear suspension...I got a 04 STI since it was brand new and im about to go on the 4 bad strut