Here is a link from BW. http://www.benzworld.org/forums/r-c107-sl-slc-class/1450267-c-r107-front-sub-frame-recall.html The first picture is of a crack in a 280SL subframe.

Mercedes gets a big fail on the subframe problem. They only covered US model 450SL/SLC and the '72 US 350SL 4.5. I know this is an old thread but never hurts to repeat the warning.

If you can find a good used 560SL subframe use it. It is updated and reinforced.