Scrubbing Bubbles.  Let it sit on the board for a while.  That's how I cleaned a pretty bad 3400c board - the corrosion eventually dissolves into the solution (I'm not sure if that's actually the mechanism, but if you leave the SB on the board for a half hour to an hour a few times it will basically float off.  Unity I think told me about it so he may have further observations on how to use it without risk.  When cleaning wires and plastic (stuff that can't really be 'damaged' like a board, I let it bathe for hours and even horrifying corrosion has totally come off with no harm to either plastic or metal.  It's pretty cool stuff.).

To wit, I reused my Kanga and 3400c power extender cables (like to the PRAM battery - technically they're part of the power boards in terms of the part numbers) despite the fact that they were totally corroded over when I started.  Left them in scrubbing bubbles in a cup and forgot about them.  The solution in the cup had a tinge of green and the metal prongs/leads and plastic connectors look like they're new.