It sounds like you've done very thorough footwork & exhausted the market, great job on really trying. I also don't see much of anything that you could rebuild or tighten up.

However, if the plastic can be removed without damaging it. Then, you may find that some items can be removed & replaced by the same pieces from a cheap improper & unrelated replacement, which just has the same diameter.

Conversely, go for "the" or "a" new faucet that fits into your future plan. The primary new faucet consideration being that it comes with an optional deck plate to cover the vanity top's holes.

This is what I've done in preparation for my new bath, where I want a single handle & single hole faucet. I found that many single hole faucets include an optional deck plate, which can be omitted later with the reinstall on the new vanity top.