Stu Ritter mentioned in a technical article in the current issue of The Star Magazine that while original Bilstein shocks / struts have an amazing life span, they do deteriorate over time, and that the rear shocks almost always wear out first.
If you have to replace them, I'd try the rears first.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".