Before I got here, I found this German forum photo-series that kinda says it all, even if you don't sprecken... http://w126.mercedesforen.de/read.php?1,313324,313452

It shows how to drill three holes through the hinge-panel along the centerline of the loose part, each about 3/16" diam., the three holes flanking the two protruding ears from the broken-off bracket. The upper/lower holes are spaced to leave a gap from the loose part of no more than 1/8", I'd say. All three holes will expose unbroken portion of the loose part's backing-plate, allowing you to plug-weld the part.

Have a fire-extinguisher or at least garden-hose on hand - hard to know what might catch fire inside that panel. If you don't want to weld there, an alternative might be to drill the same holes more or less, but step down the hole size going through the bracket and then use stainless self-tapping machine-screws, but I'm thinking for longevity the welding method is the way to go.