Your description sounds eerily like an IMPACT DRIVER, Stinker!
I consider an impact driver an essential tool for working on motorcycles, or anything with steel screws and alloy threads mating.
Galvanic corrosion between the dissimilar metals sometimes causes incredible adhesion. An impact driver often effectively extracts the screws, because . . . torque is only applied when the threads are relieved by a hammer blow.
A further enhancement toward removing stuck screws is . . . JIS (Japanese Industrial Standard) bits for JIS screw heads.
Generally speaking, Allen-head (hex socket) replacement screws are a good idea, as in carburetor screws. For the "special case" of the brake master cylinder reservoir screws, the following may be useful:
Regardless, an impact driver with the proper bit possesses considerable persuasion, when it comes to stuck screws.
Snap-On Blue Point 3/8" square drive impact driver, shown with four JIS bits: