Hello,
unfortunately you give no further details so one has to guess.
Since you ask this question I assume that the slides themselves look okay and it is only the scan which shows faces which are too red. Also, the issue seems to be only with Kodachrome. By the way, Kodachrome colours are very stable, provided the slides were properly stored.
My first guess would be the ICC-profile for Kodachrome. Did you create your own profile or did you use the one coming with SilverFast? If it is your own profile you might want to try a different profiler. There are quite some differences in the profiles created by the various software. You find examples
here. To my experience, the SF profiler has problems with some colours.
If you do not have a Kodachrome target and thus used the profile provided by SF, then you might want to try the selective colour correction tool (SCC). WIth this you can change just the skin colours either globally in the image or selectively with a mask. If you are happy with a global change you could copy the parameters of the SCC in the jobmanager.
Hermann-Josef