Outside surface rust on a sheet metal piece might make me hesitate but on a cast iron machine I wouldn't hesitate a minute if it didn't show abuse from use.
So many different formula's used in cast metal pieces world wide that all handle atmospheric conditions differently. Some will take a lifetime to turn a "conditioned dark grey to black" while the next piece from a different region of the world will turn orange just from someone walking by with a glass of water.
That thing may just clean up wonderfully with 1/2 days work with a $5 box of steel wool and an $8 can of G96 formula gun oil & carbon remover .