Thanks a lot.  I have 91% Isopropyl, which I'd been using.  I take your point about distilled water.  I wasn't so diligent with the board (I'll post updated pics in a day or two).  I had been using tap water (this is my first experiment and I got the SE/30 precisely for this reason [my SE is entirely original except for the miniscribe and I suspect it'll eventually need service]).

I've been cleaning the casing of my Powerbook 5300c battery also and I suspect (per Unity's notes also) that the continued presence of what I think is something related to corrosion is because of the use of tap water.  Though it may just be discoloration.