I have a knife care question. My father passed several months back, and as we closed out the estate, I got a couple of the old family butcher knives. I have been keeping one in a black nylon sheath, but every time I pull it out to look at it, it has a surprising amount of rust on it, especially on the sharpened edge area. I really don't think the sheath is damp. Is there some kind of oil or grease I should be putting on this blade? Just WD40? Rem Oil? Cosmoline RP-342? Blaster Surface Shield? LPS-3?