You have my attention here, The oil for metal is almost magic.I have a fabricated deck on my Ingersoll 4018 and a stamped on my JD 455 and Cub Cadet 1720. I sandblasted the original deck on the CC 1720 and primed and painted it, looked great but rusted through a few years later, possibly from reducing the thickness of metal sandblasting it down to good metal on the underside. I picked up a NOS Cub Cadet LT46 deck off eBay several years back and it is still operating fine although the paint flakes off in areas.
My reasoning for prolonging deck life is to coat the underside with used motor oil seasonally.
My brothers messed with cars from the '50's, '60's and '70's, the ones that leaked oil always had good frames under them.
As for dents and bends, pay attention to your mowing, easier said than done!