My guess is the water worked all the way into the fibers of the circuit board and needs a lot of time to dry out. Perhaps place them in an oven at low heat for a day or so. It could have saturated the epoxy and hydrated that too. Those boards aren't as sealed as modern ones and have a lot of porous sides. Just a guess. How long were they in there for?? If it doesn't go away after a good time drying you can probably "polish" it back to clear lightly with Novus 2 or a cleaner wax.