Just found this thread. I rebuild these professionally. When the wiper arm fails I solder in a replacement to the top of the horse-shoe. The actual contact is a brass half sphere. (think half of a BB). It has to be the correct length. I cut the new piece from copper / brass alloy sheets.
The next time I do one I will do a few pictures. The senders pictured can all be saved. The most lethal thing is as you expect: rust through. I can fix a few pin holes, and even line the straight parts with thin wall hard brass tube if needed but there are limits.
I am very happy to explain what I do but you have to have a very steady hand, good magnification, and exceptional soldering skills. I learned jewellery and watch repair as a kid and some of those skills and tools come in handy.
I got into this so I could make the low fuel sender used on cars with the Convenience Control Panel option work properly. I have been doing a number of Mustang and other senders for folks that like to keep their cars original.
https://desertclassicparts.com/fuel-sending-unit-rebuilding-service/