I picked it up from a recycling centre for 50 pence. It was quite dirty so I gave the caps a good clean. Then I found that the switches were a little rough, so I cleaned them out, and that helped a bit, but it was still not great. So I took off the sliders and washed them gently, then put them back up. That didn't really help either, probably because the sliders were quite dry at this point. I tried several amounts of WD40, from very little to very much, but none of them really helped all that much. So I washed the caps I tested that on AGAIN and applied a very small amount of a dry lube to it. That finally did the trick. So I took all the switches apart again and very gently lubed them. Note that it hasn't impacted the sound of the switches - this is what the board natively sounded like. It's possible these are not in a good enough condition to be representative state for white Space Invaders, but it was the best I could make out of it. I think overall it should be pretty close to what it originally was.
If it’s scratchier than a relatively modern MX black board, then as far as smoothness is concerned it’s pretty far from the original. NIB white space invaders are much smoother than recent MX black switches, and a bit smoother than “vintage” MX black or modern Gateron black switches. They’re less smooth however than green Alps or red Matias switches.
You should see if someone near you has a very good condition white space invader board you can try as a reference if you want to accurately judge the effectiveness of your cleaning method.
Getting scratchiness out of old keyswitches is really hard, and I haven’t really found a suitable method for handling the worst ones, though admittedly I haven’t put *too* much effort in. The problem is that little bits of dust/dirt/grit work their way into all the little corners, and stick pretty well to the plastic. In the worst cases the plastic itself might be abraded from use of the switches while they were full of grit, in which event fixing the problem might be nearly impossible.
Just a hand wash and the addition of some lube doesn’t cut it to clean scratchy switches. I think the most promising approach is to completely disassemble the switch and use an ultrasonic cleaner on at least all the plastic parts, then reassemble them with some added lubricant. I don’t have access to an ultrasonic cleaner though so I haven’t tried it. If you don’t have an ultrasonic cleaner, you might try fully disassembling the switches and then carefully swabbing the plastic parts out with an alcohol-soaked cotton swab, I’ve had some mild success with that method on a handful of loose switches (it’s labor intensive to disassemble and hand-clean each switch, so I haven’t done this for a full keyboard).
