OK, so while I wait to find out about getting the correct nylon hair from the UK, I experimented with new tail! So this uses a gold-plated 10x6mm crimp, and an M5 nylon washer. I had to widen the washer's hold a little, and may look at getting the next size up. But I think it's a good rust-proof method! I also need to remove an untouched G1 pony's tail, to see if I've made the tail full enough. But so far, so good.
The tail looks pretty good! I don’t have any G1’s but from that I have seen inside my G3’s, that looks fine!
I only replaced mine with plastic zipties, yours looks like it’ll really hold