washing machine squeels. Drum out of shape ?

My parents Hoover seven 1100 washing machine is squealing. I removed the door seal and found tell tale marks of the drum rubbing. I also noticed the inner drum was not concentric with the outer drum. I trimmed the seal so that the seal was not rubbing and the machine worked for one wash and then started rubbing again. Is the drum going out of shape a common problem. If I were to replace the drum would it need specialist tools ie special to type bearing puller etc etc. It is a hoover A7110 01