So are the Space Invaders that easy to break, or was this thing likely attempted to cleaned by a drunken "enthusiast" with heavy hands?
Space Invaders are pretty easy to mess up if you're ham-handed. I'd leave them alone unless you have to.
They have certain parts that are very delicate.
To remove caps, I recommend grabbing the sides and gently rocking back and forth - one of the few times that ring pullers are superior. NEVER grab the corners (like I do with most other switches) or you are likely to pull off the top part of the switch housing along with the cap. If that happens, the spring often flies away (unusual thin long springs) and the extremely delicate "fingers" or leaves are exposed. To re-install that housing top, it needs to go straight down and exactly between the leaves, with the spring aligned. It feels scary and you need to press hard, but it is not too bad once you wreck a few and get the hang of it.
I have some extras of both black and white that I will sell for $1 each + postage if you need them.
Replacing switches is quite fussy, too. There are 4 leads each, and they are thin bare wires with NO STRAIN RELIEF - how stupid is that? They probably never intended that replacements would be common. Be sure to suck out ALL of the solder and expect to ruin at least 5%-10% of them when you pull them out.