I have come across this many times. Right now I have some rusted roller bearings in an aluminum outboard motor gearcase. But I also had aluminum transmissions with stuck steel bearings. Obviously water got in and caused the galvanic corrosion. I try heat, oil, force, nothing really works some times. I once was working on an aluminum bicycle rim with stuck bearings. Heating worked as the steel and aluminum expanded at different rates. At one point the bearing just popped out from that. But usually the aluminum part is big and acts as a huge heat sink. Any tricks I should know about?