I work for a very large computer company. At one time, we spec'ed our
components and PC boards to withstand a cycle in a dishwasher
with Calgonite detergent.

Soaking a PC assembly will (like the poster mentioned) cause
other components to absorb water. Bad thing. Aluminum electrolytics
would likely take it the worst. PC boards are washed typically with
deionized water then run through an "air knife" on a conveyor, then hot
air dried during the manufacturing process.

The problem you'll likely run in to is the keyboard membrane switches
having contact problems but hey, what you have doesn't work so whadaya
got to lose?

I'd opt for a dishwasher cycle (including dry) then placing the board
in a warm area for a while to evaporate any other moisture trapped.
Problem is each button on the keyboard has a separate switch with a
silicon rubber "spring" and each will likely need to be removed.and
replaced. Not fun at all.

b.