Compress a wet, warm towel around the beater shaft for 10 minutes.
Re-warm it after the 10 minutes, put it on again and let it set for 1 -2 more minutes.
This will re-warm the aluminum, causing it to expand. After this time, try to wiggle and remove the beater.
If the beater does not come off with the hot compress, try applying a small amount of mineral oil to the beater shaft above the beater and in the slot where the beater attaches to the beater shaft pin.
Allow the oil to sit on the beater shaft for several minutes, and remove the beater.
If you don't have any mineral oil, use a vegetable oil cooking spray.
If you use vegetable oil, make sure to clean the beater shaft very well after the beater is removed because it can become very sticky over time.
Once the beater is off, soak the beater in hot soapy water and clean out the beater cavity very thoroughly using a wooden skewer to remove any build-up of food particles or oxidation residue.
If this residue builds up in the beater cavity where it attaches to the beater shaft it can be difficult to remove.
You may also want to apply a little mineral oil to the beater cavity before putting it back on the beater shaft.