Meh, ferric alloys don't fail in cyclic loading as long as you keep the magnitude under about 60% of the yield stress. Aluminum is not so, which is why airframes always eventually have to be retired. A steel car body can go pretty much forever as long as you protect it from corrosion.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.