Restoring PSX Manuals Slightly Hardened by Moisture?

[Kyle15]

I've had my copy of Klonoa that I bought at Gamestop for a little over a year now, but something about it is bugging me. The manual is slightly hard, almost as if moisture formed in the case during shipment to the store. There are some wrinkles in it too, but is mainly just quite stiff.
Is there a technique out there that can restore these things to a better shape? I know that it may be impossible, but I thought I should still ask just to be sure.

Thanks!