[Raleigh]

I don't think I'd do anything in your shoes. Just don't ever try to put the plug in the speaker with the power on, else you might put the full rectifier voltage on the voice coil while you're wiggling it to orient it right. You shouldn't do that anyway.

I'm not sure where the other end of that rivet is, but if it is on the back side of the plug, you could drill it out, make a new cardboard piece with the holes in the right place, and put it back with a self-tapping screw just a tiny bit larger than the hole.

Or you could glue the new cardboard piece in place. There are some tenacious glues that will probably hold well. Aleen's Tacky Glue seems to bond well to cardboard and to plastic. I used to think it wouldn't bond well to plastic, since it looks just like Elmer's, but it has bonded to whatever kinds of plastic I've used it on. I don't know how it would bond to that particular plastic, but since it doesn't bear any load there's a good chance it will be plenty good enough.