backup light switch, 63 push button

I would not drill it. I took a close look at mine and I don't think drilling is a good idea. Now something to try is to remove the switch from the mounting bracket by prying up the 4 little tabs. Once the switch is off, spray the under side with contact cleaner and move the switch back and forth. I got a lot of black gunk out of mine which was carbon on the contacts. Seeing how these are 46 years old, dirty contacts seem to be about the only way they would stop working apart from mechanical failure or breaking. Assuming your switch is still intact and the spring is working, cleaning the contacts may get it working electrically again. Check the switch with a tester to make sure it is passing the current. If it is, something else may be loose. There is a connection behind the driver's kick panel for the wire to the trunk so you may wish to check that as well.