First step (after cleaning the case etc) will be to fix the keyboard.
Many of the keys stay down when pressed, and some appear to not work at all.
Firstly, I removed the keycaps completely, and cleaned the dust and grime away from underneath the keycaps. I could see with the keycaps removed the stems of the keyboard switches, which I've identified as Alps SKCC Tall Cream - thanks to this site.
The mechanism of these keys seem fairly simple, but disassembly for cleaning further is not simple - the keys must be desoldered from the PCB, as they are clipped into a metal plate.
I sprayed the keys with contact cleaner, and "worked" the keys, pressing and pulling the sticky ones up and down. This had the desired effect for some, but the enter key were very sticky, and are essentially unusable without further lubrication.
In total, there are 4 keys on the keyboard that need replacing - the Open and Closed Apple keys, the Enter key and the number 6. I will touch on the Open and Closed Apple keys in a seperate post, as these keys caused a further problem with the machine failing to boot properly.
The SKCC keys are relatively available online, so I have purchased 10 from eBay, and will desolder and replace the keys when these arrive.