According to my old MoToR'S Manual and FSM's, the coaxial
type power steering, '57 and earlier, uses ATF Type A and
the constant control power steering, '58 and later, uses
special power steering fluid.
--Roger van Hoy, '55 DeSoto, '58 DeSoto, '42 DeSoto, '66
Plymouth, '81 Imperial, Washougal, WA