Oil Pan nut
I just changed the oil and took off the 1/2" nut and used a pan to catch the oil, when I was finished draining, I looked at the nut and sifted thru the used oil for a copper washer or some sort of seal and found none. I looked at the nut, cleaned it and it looks like there is a rubber gasket seal built in. Is that the way they come. To be safe I am going to get a new one from the dealer for spare for future oil changes.