1. The old ones fitted had a little slot to lever the clip open with a small screwdriver. The ones on the boot didn't.
2. They were exactly the right length and clipped straight on. The boot ones needed compressing a few mm and that needs extra hands!
3. Same old broom handle did the support job well from the cross-member at the front.
The bonnet now opens easily having a little more support but slows down at the exact same point that I needed to lift from before.
Now it just rises very gently (unassisted) from there over that last few inches in about 15 seconds. Very satisfying. And no bad noises!
