It has been over 24 hours since, I did the flush. The keyboard is partly working now. "R" key works fine, the rest of the keys go berserk or random. The controller seems to be working fine, since cap/scroll/num lock light up if I were to enable it on my other keyboard (Logitech Elite USB).
I think the membrane just needs to dry itself more. I have play to the waiting game. FYI, I'm using my system as the gentle "space heater".