The switch is an extraordinary little piece of engineering. If you ever drill off the rivet heads (from the four items in the red & blue boxes) & crack one open, beware of flying springs & parts. There's compound ratchets & spring-loaded centering elements & switch contacts... there's a lot of stuff crammed in that case.
You can see the detail of how I "salvaged" the black plastic piece. I had a machinist do the fine work of drilling the holes & providing the tiny screw. You can see that the "arm" is not exactly where it was when it started life. The break point is under the metal "patch" but it was a good first try & in fact it works well. If I repair any more I will try to get the geometry as original as possible. The pointy tooth on this arm is what catches & pulls the high-beam toggle ratchet.
Note that the pieces are not identical; the black one has the intermediate bump. The white one may break someday, too, but I don't think it endures as much stress. I forget what I was trying to show with the red outlines.
Reassembly requires about 5 hands to hold all the spring-loaded pieces in place while you lower the top half of the case onto it all. As far as holding the case together, I had my machinist tap tiny screws into the 2 things in the red box in the top picture (they need to be re-used, since the hex end of each is where the screws go to secure the switch into the steering column) & then I just used tiny threaded rod with small nuts & washers to take the place of the 2 rivets in the blue box. Thus, the case is held together in the 4 original places.
Having performed surgery on this device, I can definitely say that you'll extend its life by not flashing-to-pass (which rapidly & repeatedly stresses the delicate arm) and by always switching to low-beam before turning the stalk to switch off the headlamps (you'll manually disengage the high-beam ratchet before disengaging the low-beam ratchet, as opposed to both stresses at once).
I also strongly recommend partial rewiring of the headlamp system to include relays to relieve the multi-switch of the burden of flowing some 20 amps. I haven't done this yet, & as a result I really don't drive the convertible after dark.