This is where the leak was coming from which lead me to biting the bullet on this resto.... common wisdom is the Dutchman panel but as you can see it's solid but does have surface rust, so I'm stumped as to where water was getting in at. Kind of thinking all I needed was a new weather strip around the trunk?!?!?!
Examining your pics on the rear window leaks. I'm still not sure which hole you are referring to. I see a 1/4" hole a couple inches below the window. That hole is where the clip goes through the metal and holds down the stainless trim for the vinyl. The other pic shows studs but if you look in the trunk, they should come out. At least this is how my 70 is. Maybe in 73 they welded a solid stud on the top for the clip to slide onto. Maybe someone who knows the 73s can provide more info. If nothing else, examine the backside. If smooth, it's a welded stud. I'm guessing the is a small nut holding the stud clip on.
If it is a stud, then obviously one of yours rusted away. I would buy a tool and remove the rear window next. It's easy and it has to come out for repairs anyway. Next, remove all the clips next to the glass that you can (held in with Phillips screws). Then clean the whole window ledge out and inspect. You will probably find a few rust holes.
Any trim clips that don't come out can be ground out easily.
Your Dutchman panel looks good. I would not replace it. I would identify the holes, cut away rusted metal and weld in new metal. It's not that bad a job. Even if you pay someone to do it, shouldn't cost much.
