the pillow ball *joint* while stiffer, does allow for rotating movement in the joint with out constant stress on it and on the other pieces it's bolted to. the polyu are under constance stress.

this cracking isn't something that has or will happen over night. this is happening on cars that have had them on for 2+ years.

also these cars (z32) are 500-700lbs more than the typical s13/14, so it might/or might not take longer for the cracking to take place on the s-bodys. but it will sometime.

none of the Z32 ppl i know of, or heard of has used the whiteline bushing, they may have a better flex to them, but the ES bushing are the ones causeing this stress cracking.