I have a really good guess from your vid about the problems. It's the plastic of the case. The cracks/cuts coming off the switch are likely stress fractures from screwing down the retaining ring that holds the switch in place. That surface is not flat there either which would make it worse. With some plastics (flat) you could install a switch without reinforcing both sides (small plate or something) but it would probably fail over time from the stress of pressing the button and not pressing it exactly perpendicular.
If that's a drilled hole then the fractures could have come from that also but I'd guess they happened when the switch was installed. It's possible they weren't even there when the switch was installed and just slowly developed over a day or days just sitting there from the pressure from the retaining ring.
The epoxy smudges are just that. Touch it and you can't fix that without buffing a new finish on the plastic (not easy because of the next part).
My guess on the "melting". Very likely the result of using a dremel tool. If you try to cut plastic like that with most any sort of high speed tool it will more melt it than cut it. envision a laser cutting
through butter. It doesn't cut it melts. If you do that then cleaning the slag is like cleaning the chemical smudges. You would have to cut off the slag with something like an exacto blade and painstakingly refinish it to a gloss again. It's not easy, like just hitting it with a dremel with a buffing wheel because ... it melts so easily.
Also because of the above it's extremely difficult to cut precision holes. I expect the epoxy build up is mainly because of that and secondly for reinforcement.
Just some speculation and guesses as to the mechanical and cosmetic issues.