I have had a couple of stuck square taper crank arms. Know the first thing I do is spray some Kriol penetrating oil into the taper and let tit sit overnight. I have also warmed the aluminum crank with a hair dryer. Does not always work. Once as a last resort I used a flywheel puller. Scary but I was surprised it did not damage the crank arm. No issues after using the Kriol. But then the Kriol may prevent galling causing the parts to stick together.