I have a set of .250 dies, older than dirt. They'd gotten kind of a dark patina to them, noticed when cleaning out the die drawer, rusty? or whatever. I tore them both down and used the Dremel tool and one of the steel brushes, on the bullets stem and decapping stem. Then I took a drill bit and wound a gob of 0000 wool around it, went inside the die body and ran it around in there a bit, to clean any and all gunk out. Then lightly applied some synthetic oil on the die bodies and wire brushed them off, wiped them down and applied some of the oil inside with a Q tip, assembled everything and put away. Simple solution. While disassembled, I took a drill bit and drilled, lightly, inside the bullet seating stem, to remove a tad bit of metal. When reloading Hornady AMax bullets, the plastic tip gets bent over, not enough room for the tip, removing just enough metal relieved this situation.