A few months ago I bought a 1949 Case SC tractor with a stuck engine. The previous owner had filled it with diesel fuel and had been sitting for months. I got it for a lawn art price because he gave up on it. Long story short, I drained the 6+ gallons of diesel fuel out, took apart what I could and found the piston that was stuck and filled just that cylinder with the Harris 30% white vinegar. About 36 hours later, the stuck piston was out. I don’t think it harmed the AL piston but it raised hell with the corrosion and did reveal all the pitting caused by the corrosion. I’m sure other methods will work, this vinegar one worked great for me.