Tension arm bushing, the stock gel-filled unit is prone to early failure. I haven't heard of many going early aside from that one. The rear suspension, although loaded with bushings, is far more durable than previous generations, especially the E46 RTAB ridiculous replacement schedule.

realoem.com and penskeparts.com have pretty good diagrams of all of the bushings, and powerflexusa.com has a list of those bushings they offer to give an idea, I believe there are over 30.

 

thanks

 

Lower front control arm bushings start to show play at about 30k miles on these cars.