preserve heartwood?

Howdy, all you guys and gals and JOAT too;
I got a very pretty bitch I mean birch board from my SWMBO's granddad. He values it 'cause it has a wide band of reddish heartwood the whole 7' length, so I need to keep that in anything I make from it.
The board's 9" wide and the heartwood is about 3" wide, and in the middle.
I decided on a sort of tradesman's box or small chest or trunk, three little drawers over one wide one in the front.
It's going decently well, but that dagnabbed heartwood is like working with graham crackers. It's finally assembled, and already cracks are appearing in the heartwood along the grain.
Is there some way I can slow down or prevent the heartwood from what looks like disintegration? Sealer?
Filler? anything?
Thanks even if I'm doomed-
James http://

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