Sagging rear end on 1986 300SDL ??

I realize that rear ends tend to sag with age, but there are relatively simple operations for that problem. With my 300SDL, it seems to be a more difficult problem. I continue to sag even after replacing my differential mount and having OK shocks on the back (i didn't change them, but they only bounce once after compression.) Should i replace them anyway (they probably have not been replaced in a while)? or are there other common wear parts that i have neglected to replace? I would really like to see tops of my rear tires.....Thanks for the help.

Scott