The W210 uses the same design ball joint as the W202. I have a W202 with 145,000 miles on the clock and it still does not need ball joints. I have a W210, but it only has 40,000 on it, and I have yet to have any clunking. What I do know, and this has been brought up by Steve Brotherton, who should know, is that the "hydraulic" lower control arm bushings are a weak point, particularly with larger than stock wheel/tire packages. I would question, and have them show you on the rack, any ball joint diagnosis.