So I found a piece of 1/8" stainless welding rod and started making a replacement spindle.
I drilled a 2mm hole through the end where the spring attaches.
Then cut to length, heated and hammered the end to a dome.
Put the plastic/copper tube bits back on the spindle, found a stainless spring to replace the original rusty one and re-assembled. One rear brake switch which won't rust.