The very best penetrating oil is a 50-50 mixture of acetone and Automatic Transmission Fluid.
Try that first. It beats WD-40 by a mile.
If that fails, the next thing to try is heat. Heat the machine screws almost to red heat. Then touch a candle to the head and let the wax melt. The molten wax will be drawn into the threads by capillary action and will lubricate them.
You do not need the tat-tat-tat of an impact wrench to break loose a stuck bolt. You need one very stout impact. After the wax trick, put a cheater on your Allen wrench, and take all the slack and spring out of the system with one hand. Hold it in that position and hit it HARD with a heavy hammer. This can work miracles.
If push comes to shove and you have to drill it out, go to a very good tool store and get a left hand drill of the correct size. Frequently just drilling it out with a left hand bit will loosen the bolt. Of course you have to run the drill in reverse with the left hand bit.
Steel screws into Aluminum + time = chemical bond, no?. Do any of these penetrating oils actually affect the bond? It seems unlikely. But, maybe they keep the bond areas from reforming if one can gradually break some free?
The 50-50 mixture of ATF and Acetone is interesting too. The acetone would flash off quickly (unless it gets down into the threads.) Maybe it “wicks” the best? Slowing flash-off may be at the heart of mixes also containing mineral spirits or turpentine. I would wonder if xylene might not work well, to mix with ATF? Xylene has a slightly “oily” characteristic to it, to begin with.
BTW, PB Blaster should be available at Wally World, Home Depot, Menards, Lowes, and many hardware stores and farm supply stores.