"Has anyone successfully replaced the threaded studs on the handles, that snap off, when the stud becomes rusty?"
This is the Archilles' heel of the door handles and rear tail lights. On the door handle, the stud is cast with the rest of the handle and made of whatever alloy the handle is made of.
You can try and cut off the stud flush, drill and tap the hole, screw in a bolt with some thread locker and cut the head off the bolt.
I will let you know how my fix works. I have tried to types of metal repair. The first is a material that is a malleable metal putty and has worked for one patch and now I am trying JB weld which seems stronger. I cut off the stud, drilled out a larger hole and then took a bolt and cut off the head to match the length. I wonder if brazing would work. psg
Since the handle is made of a non ferrous alloy, welding or brazing won't work. However since it's a relatively soft alloy, drilling and tapping is easy. Just clean the hole and bolt well with alcohol, benzine, acetone, or fingernail polish remover then use some form of thread locker when you screw the bolt in. Your wife's fingernail polish will work as a thread locker. Matter of fact, just use all her cosmetic products for this fix.