I've owned a DeLorean since 1999. It's body panels do not rust or discolor at all, and the car has been stored outdoors under a cover for most of its life. The panels are "plain" 304 stainless steel, the same grade that is used in kitchens and food preparation machinery. As far as I know the only more corrosion-resistant grade is 316, which is used in medical equipment and smaller items where cost is less of an issue. The panels on the cybertruck are some "secret" alloy called 30X. It's probably very similar to 304, but the work hardening process that Tesla says gives the panels more strength may also lower is corrosion resistance.