I've not seen an SD door lock, but it can't be too different from other MB locks of the era. With 190/124 locks, the lock assembly is made in two sections, held together with roll pins. If you drive out the roll pins (they don't have to be drilled in this case), the two sections come apart. Then you just have to rotate the cylinder 180 degrees and pull. Post some photos of the handle and I may be able to tell you more. I'll be posting a page on my 190 locks shortly, I just haven't had time to work on it.