Welcome to the forum!
Because of the kits' historical value, replacing the inner shell would detract from over-all value and, no more 'original.' I would imagine that an experienced drum repair tech, or even a good cabinet-maker, would be able to execute a good repair of the crack.
I'm not a PC fan per se, although I always loved Genesis. I do recognize the historical significance of the kit though and I congratulate you on a great acquisition. Sorry to hear you're letting them go. Should do very well for you at auction. Do you have any form of provenance (documentation) for the kit? If not, might be a good idea to have it in-hand before auction time. It'll help boost value tremendously. In any event, thanks for sharing and best of luck with your sale.
John