126 sagging or listing?
If you have a 126 that sits low in the rear or has one side lower than the other in the rear, try this.
Check the gap between the spider plate and the subframe mount just ahead and inboard of the rear jack points. The gap should be even all the way around. I just fit new mounts and the gap is almost 1cm (I can fit a finger through most of the fingernail). It was less than 5cm with the old mounts (I could fit a finger up to a third of the fingernail). I expect some settling of the new mounts so 1cm might be more than I should expect from used mounts.
My 300SE leans to the left and the gap on that side varies between 3cm and none. Hmm...
User Thomaspin has instructions for replacing subframe mounts. There is a link in his sig line on all his posts.