i have seen the switch inside the similar model, and taking it apart can be easy or very hard depending on if the glue is set and in the right places on the threads.
a little heat from the heat gun worked to free it, of course then making it to hot to work with. on one i had to drill out the holes bigger and stuff (brittle) drill bits in to get the threads loose, because everything else BENT i stuffed in there.
in the mods threads they talked about a locktite solvent that frees up locktite, i have never tried it.
the flatblade screw looking indents are indeed nothing, mabey there to just confuse us :-(
with beer/soda/sugar, you need to Rehydrate the stickey substance, then move it away.
so i would soak it in 99% Alcohol for 3 hours, then try and get the alcohol out, use a compressor or something, then use silicoln spray , the light very solventy non-enviromental kind, which is harder to find, to finish up.
inside there is the BIG back plunger like you see, then a spring JUST to retract the big button plunger, then a seal (that on mine was broken) then there is a 12mm type round small switch , that is the actual switch behind the mask. you might have to get your solution back that far, to free up the switch IF the plunger is moving fine, but the switch is not. if its just the plunger, then , you should be able to free it up without dissasembly, just get stuff up in there and Leave it for time. like in a dixie cup full of alcohol (no not more beer
the system basically has 3 spring retractions, the plunger retract spring, the spring in the switch itself, and the springy seal that is supposed to keep beer out, its pretty hard to keep that from retracting , what was it microbrewry with pulp hops
at any rate, rehydrate the beer for TIME, then move the rehydration solution out. if you use water to rehydrate the beer, then you use alcohol to get the water out, then silicoln spray to finish up , which leaves a very thin oil to lubricate and protect.
