To be fair, there is no mention in history how much silver is actually required. Just that Silver needs to be present. So it's theoretically perfectly fine to make an oil that can coat a weapon with the metal.

The reason why that Leon wants to avoid paying for silver weapons, is it's too permanent to gild (plating) a weapon with it the sharp edge would need to be covered and will be dulled very quickly. It's too expensive, which makes it impractical outside of some very rare cases. And it's Softness is actually comparable to copper in softnes, which limits the length of a pure silver weapon to about an arming sword or less. And it can bend and break pretty easily.

If you asked him what he thought of the 'professional' monster slayer's she was rolling with. He'd call them dumbasses that are setting foot into an actual professional's territory.

Sides, he admited he's no monster slayer so his knowledge is questionable. But he never said he hasn't encountered any of the undying in his life *wink* (not implying that he killed one, just that it's not uncommon to see them in the criminal underground or to get contracted by em)