Posted By:
Dave G...it depends what the gunk is.......if its congealed rubber band...forget it unless its got very brittle.
If its paper adhesion, do as Barry suggests, try some non-expensive cards first to see if the colors are fast.
I would warn against spot soaking - this inevitably leads to uneveness across the picture surface - and some of the A & G series are heavy in a dark glue or what ever was used to hold the cardboard layers together, and this leaches and stains. soaking the whole card is more preferable. But I'm sure others will contribute other ideas.
As also I'm sure this will being out the righteous condeming the "demon soaking".