There's some theoretical improvement due to saturation of the iron core, although it would probably be prohibitively expensive to go from the iron core to an air core with the same values. You may actually have to add in series resistance to match the dcr in those iron cores from an air core. I'm going to guess you're looking in the $25-40 range for each. If both of the ones you have measure well, then I wouldn't bother, but that's your call. I see no reason they shouldn't still be to spec.