the blade adapter will keep breaking also if the fly wheel key is broken. and make sure your blade is balanced - that may have been why one, or the other, or both broke in the first place. you can get a new fly wheel key for a few bucks at ace hardware.
lowes sells the blade adapter for about $10. oh, and both stores should have a blade balancer. looks like a devo hat, like a terraced cone shaped thing.
link for flywheel key replacement...
http://www.youtube.com/watch?v=vWcIiZtvbug
matt
November 2009