Bushings

When everyone here does a suspension upgrade, it's usually some combination of springs, anti-roll bars, and shocks. One of the things they did with the 25th Aniv Edition GTI is to use stiffer bushings in the rear suspension (I'm not exactly sure where). Apparently this has the effect of controlling camber changes in the rear wheels under cornering, and, therefore preventing understeer
Has anyone here done this themselves? Does anyone sell the necessary parts?