Usually i throw away and use a metal one. My boy’s car had been leaking from drain bolt. i asked if he replaced the washer when he changed oil. He didn’t so i told him to replace it. He ended up buying a whole mew drain bolt with a plastic washer and used that. Didnt have a metal one on hand. Are these actually able to be used or should he get a metal one, its still leaking which is why i ask. Unless he’s not tightening enough which i doubt is the issue. Thanks people