My poor xcross is suffering from a bad case of "heavy mutha jumpin on me" soft deck.

I just finished looking at boardlady's site, and am wondering whether I go the whole hog, and 'cut-er-open' (might not be a very economical remedy, the board is about 6yo, or should I look at injecting some expanding foam, or epoxy? (for starters....is this even compatible with the foam core in the board?)

Anyone successfully managed to repair this?

At the moment the area is between front & back footstraps about 350mm dia, and the deck hasn't cracked, or leaked.....movement is about 4-6mm in compression, and although I noticed it a few weeks ago, only after sailing in heavy chop yesterday has it become very noticeable.