Disassembling White Apple Wireless Keyboard

Okay, so after nearly seven years of continual use I eventually spilled some liquid on my white Apple Wireless keyboard, which is annoying as I thought it'd only splashed the keys as I dried it off quickly, but obviously something got inside.

Anyway, it seemed fine after that until eventually I started having trouble using the Apple keys, I thought it was just a weird system glitch and shut-down for the night. This morning though I switch it on and, while it connects okay, now none of the keys work, and I can see a tiny amount of liquid inside.

While I do have a spare keyboard of the same type, it's absolutely filthy, so either way it looks like I'll need to disassemble a keyboard, but I can't find a screwdriver that will fit. I even have a set of hexagonal screwdrivers but none of them are quite small enough; I really hate how Apple seems to delight in using fittings nobody has a tool for, as disassembling a keyboard is surely bog-standard user maintenance!

What I need to know though is what type of screwdriver exactly am I looking for these keyboards? They're the older Apple Wireless keyboards made from a clear plastic tray with white keys, full-size keyboards.

 

With the clear keyboard it should be easy enough to tell if it's still wet, hopefully it isn't already broken from my turning it on earlier (when I discovered the problem); it connected fine so the bluetooth chip and power can't have any trouble, must be something interrupting the signal for the keys.

Anyway, if I can't find the tool to open it properly I'll give water a try; is it okay to just submerge it when doing this, minus batteries of course?