Our 85 300D was cracked in the same place. the metal can be tweeked just so many times and it will start to crack. that just shows you how much torque the motor puts on the regulator and sheet metal.
looks like there is a crack also diagnally going up to that upper hole. If the crack is cought early enough, a hole can be drilled at the end of the crack and then welded. this will keep the crack from growing. either way it will need to be welded.
I was thinking of cutting out a piece from another door (PNP) and lay it over this section and weld it to strethen it.
The wollowed out hole is from the nut coming loose and letting the stud work in the hole.
Charlie