My 2 cents:
This bothers me. Something doesn't seem quite right.
I have never heard of any Mercedes going through two sets of ball joints in 70k miles! Let alone one set in 23k miles.
I realize the 210 series is a very different car than our 190e, but it has gone over 220k on the original ball joints and I just checked them and they are still good.
Do you drive on unusually rutted roads, weird pavement or railroad tracks?
Are you sure that is what it is and that is what was replaced previously?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)