I agree up to... new parts shouldn't need cleaning. And cheapo hobbyist-grade RF and audio connectors often have a weird chrome + some kind of oil or varnish s

I agree up to... new parts shouldn't need cleaning. And cheapo hobbyist-grade RF and audio connectors often have a weird chrome + some kind of oil or varnish surface finish that just won't clean off or solder and flux is a godsend for those. That said, I let someone borrow my bottle of liquid flux about a decade ago and have never bothered to replace it.